(Ufllumliia  UniurrBity  ^     ^^ 
iiiJhrUIitgof  Npui  ^ork 


l&tfnmtt  ICtbrarg 


PUBLIC  HEALTH   LABORATORY  WORK 


Digitized  by  tine  Internet  Arcinive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/publichealthlabo1914kenw 


PUBLIC  HEALTH 

LABORATORY  WORK 


BY 

HENRY  R.  KENWOOD,   M.B.,  F.R.S.  Edin. 

D.P.H..  F.C.S. 

CHADWICK:     fROFESSOR    OF    HYGIENE    AND    PUBLIC    HEALTH,     UNIVERSITY    OF    LONDON  ;     .MEDICAL 

OFFICER   OF    HEALTH   AND   PUBLIC   ANALYST    FOR   THE    METROPOLITAN     BOROUGH    OF    STOKE 

NKWINGTON  ;    EXAMINER    IN     PUBLIC    HEALTH    TO    THE    ROYAL    COLLEGES    OK 

PHYSICIANS    AND    SURGEONS,    LONDON,    ETC. 


SIXTH  EDITION,  WITH  ILLUSTRATIONS 


PAUL  B.  HOEBER 

67    &    69    EAST    59TH    STREET 
NEW  YORK 

1914 


[Printed  in  England.  | 


PREFACE 


The  first  edition  of  tiiis  book,  while  dealing  mainly  with  chemical 
matter,  contained  a  useful  resume  of  public  health  bacteriological 
work,  and  this  contribution  was  continued  in  subsequent 
editions;  but  it  is  felt  that  the  time  has  now  come  to  exclude 
all  but  occasional  references  to  bacteriological  matters,  in  order 
to  keep  the  volume  within  the  compass  of  a  handy  laboratory 
guide  to  the  chemical  branch  of  public  health  laboratory  work; 
for  the  needs  of  the  public  health  student  in  bacteriology  are  now 
fully  provided  for  by  several  excellent  laboratory  works. 

The  book  does  not  describe  a  large  number  of  methods  to  the 
same  end.  It  has  always  been  the  aim  of  the  writer  to  simply 
and  sufficiently  describe  selected  processes  which  experience  has 
proved  to  meet  satisfactorily  the  requirements  of  the  public 
health  worker. 

In  the  section  on  Food,  while  prominence  is  given  to  adul- 
teration which  raises  the  presumption  of  a  danger  to  health,  it 
has  not  been  judged  wise  to  exclude  all  reference  to  other  matter; 
for  the  public  health  student  is  still  required  at  some  examination 
centres  to  show  a  knowledge  of  laboratory  methods  for  the 
detection  of  sophistication  which  has  no  bearing  on  health,  such 
as,  for  instance,  the  methods  which  serve  to  distinguish  between 
butter-fat  and  other  fats  used  as  substitutes. 

I  have  to  acknowledge  gratefully  my  indebtedness  to  Mr.  F. 
Marchant  for  assistance  rendered  in  the  preparation  of  this  new 
edition;  and  I  have  also  to  thank  Messrs.  Townson  and  Mercer, 
Messrs.  Baird  and  Tatlock,  and  others,  for  the  loan  of  blocks. 

H.  R.  K. 
London,  1914. 


CONTENTS 


PAGE 

INTRODUCTORY  NOTES    -----         i 

PART  I 

THE  CHEMICAL,  MICROSCOPICAL,  AND  PHYSICAL 

EXAMINATION  OF  WATER  FOR  PUBLIC 

HEALTH  PURPOSES 

CHAPTER 

I.    THE   COLLECTION   OF  SAMPLES INFORMATION  REQUIRED 

AS  TO  SAMPLES QUANTITATIVE  EXPRESSIONS  -  19 

II.    THE    PHYSICAL    CHARACTERS    OF   WATER  -  -2^ 

in.    CHLORINE  -  -  -  -  -  -         31 

IV.    HARDNESS  -  -  -  -  -  "37 

V.    THE    POISONOUS    METALS  -  -  -  -         44 

VI.    CALCIUM     AND     MAGNESIUM     SALTS SILICA SULPHATES 

PHOSPHATES  -  -  -  -  -  54 

VII.    THE    SOLID    RESIDUE  -  -  -  -  -  60 

VIII.    THE      EXAMINATION      OF      SUSPENDED      AND      DEPOSITED 

MATTER  IN  WATER  -  -  -  -  -  64 

IX.    ORGANIC    MATTER    IN    WATER  -  -  "  '  75 

X.    WANKLYN'S    PROCESS  -  -  -  -  "77 

XI.    THE     OXIDIZABLE     ORGANIC    MATTER E.     FRANKLAND's 

PROCESS  -  -  -  -  -  -  86 

XII.    OXIDIZED    NITROGEN    (NITRATES  AND  NITRITES)-  -         92 

XIII.  THE    GASES    IN    WATER       -----       loi 

XIV.  COMPOSITION    OF    WATER    FROM    VARIOUS  SOURCES THE 

OPINION    ON    WATER   SAMPLES  -  -  I  ID 

XV.    SEA  WATER  ------  130 

XVI.    ALKALIMETRY  AND  ACIDIMETRY ICE MINERAL  WATERS 

ANALYTICAL    SCHEME  .  -  _  _  136 

PART  II 

THE  ANALYSIS  OF  SEWAGE  AND  OF  SEWAGE 

EFFLUENTS         -  -  -     i43 

PART  III 
SOIL  EXAMINATION  -  -     157 


Vlli  CONTENTS 

PART  IV 
AIR  ANALYSIS 

CHAITER  TAGK 

I.  THE    NORMAL    CONSTITUENTS    OF   AIR — OXYGEN — EUDIO- 

METRY  -  -  -  -  -  -       173 

II.  CARBONIC    ACID     -  -  -  -  -  "179 
III.    THE    ORGANIC    MATTER    IN    THE    AIR             -                  -  -       I92 

IV.  AMMOXI.\ — MARSH  GAS — CARBON  MONOXIDE — SULPHUR 
COMPOUNDS — NITRIC,  NITROUS  AND  HYDROCHLORIC 
ACIDS — PHOSPHURETTED  AND  ARSENIURETTED  HYDRO- 
GEN       -------       195 

V.  OZONE — PEROXIDE    OF    HYDROGEN  -  .  -       206 

VI.  SUSPENDED    MATTER    IN    THE    AIR  -  -  -       2IO 

VII.  THE  CHARACTERS  OF  THE  AIR  COLLECTED  FROM  VARIOUS 

SOURCES — BACTERIOLOGICAL   NOTE        -  -  -       216 

VIII.    SCHEME   FOR   THE   DETECTION   OF   GASES   WHEN    PRESENT 

IN    LARGE    QUANTITIES  .  .  -  .       221 

PART  V 
FOOD  EXAMINATION 

I.    COMPOSITION    OF    COW'S    MILK  AND    OF    OTHER    MILK  -       225 

II.  THE    ANALYSIS    OF    MILK  .  .  -  -      229 

III.  THE    SOPHISTICATION    OF    MILK — MILK      PREPARATIONS 

■      MILK    STANDARDS BACTERIOLOGICAL    NOTE      -  -  242 

IV.    BUTTER — CHEESE LARD  .  -  -  -  253 

V.    CORN — WHEAT-FLOUR         -----  266 

VI.  BREAD        -------  278 

VII.  THE     AVERAGE     COMPOSITION     OF     OTHER     FLOURS     AND 

MEALS THE    MICROSCOPIC    CHARACTERS    OF    THE    DIF- 
FERENT   STARCH    GRANULES        -  -  -  -      284 

VIII.  MEAT PARASITES     OF     FLESH — POISONING     BY     FOOD 

MEAT  PREPARATIONS  -----  293 
IX.  ALCOHOLIC  BEVERAGES  -  -  -  -  "S^S 
X.    VINEGAR — LIME   AND    LEMON    JUICE — MUSTARD — PEPPER 

SUGAR — HONEY            -----  332 

XI.    COFFEE — COCOA CHOCOLATE         .                  -                  -                  -  343 

XII.    TEA INFANTS'    FOODS       -----  35O 

XIII.    PRESERVED    AND   TINNED    PROVISIONS        -                  -                  -  358 

XIV.    CHEMICAL  ANTISEPTICS  AND  COLOURING  AGENTS  IN  FOOD  366 

XV.    ARSENIC     IN     FOOD — ARSENIC     IN     WALL-PAPERS,     ETC. 

RAG    FLOCK          ------  387 

PART  VI 
THE  EXAMINATION  OF  DISINFECTANTS     -     399 

INDEX  _._---       413 


LIST   OF    ILLUSTRATIONS 


Plates  I. -IV. — Objects  found  in  Impure  Water  (Variously  Mag- 
nified) . 

1.  Water-Bath  and  Drying-Oven      -             -             -             -             -  2 

2.  Chemical  Balances  (Townson  and  Mercer)               -             -             -  3 

3.  Water-Bath  with  Constant  Water-Level  -             -             -             -  6 

4.  A  Specific  Gravity  Flask  ------  7 

5.  The  Westphal  Balance     ------  8 

6.  Soxhlet's  Fat-Extraction  Apparatus        -             -             -             -  10 

7.  The  Spectroscope  -  -  -  -  -  -11 

8.  The  Polariscope    --  -  -  -  -  -I3 

9.  A  Burette  filled  up  to  the  10  c.c.  Mark      -             -             -             -  15 

10.  Wynter  Bl3rth's  Tube  for  collecting  Sediments   -             -             -  64 

11.  Showing  the  Sediment  of  a  Pond-Water,  a  Sample  of  which  was 

collected  in  the  Early  Spring     -             -             -             -             -  65 

12.  Vegetable  Tissue  -  -  -  -  -  -67 

13.  Ciliated  Embryo  and  Cercaria  Form  of  Distoma  hepaticum           -  73 

14.  Apparatus  for  Wanklyn's  Process             -             -             -             -  79 

15.  Apparatus  for  Thresh's  Process  -  -  -  -  -105 

16.  Collecting-Bottle  and  Tin             -                           -             -             -  125 

17.  Ice-Box      -             -             -             -             -             --             -  125 

18.  Apparatus  for  Adency's  Process                  .             -             -             -  150 

19.  Arrangement  for  Registering  the  Varying  Levels  of  the  Ground- 

Water                   -             -             -             -             -             -             -  158 

20.  Knopp's  Soil-Washing  Cylinder  (Townson  and  Mercer)     -             -  161 

21.  Fraenkel's  Borer  -------  170 

22.  Hempel's  Gas  Burette  and  Absorption  Apparatus           -             -  I75 

23.  Hempel's  Double  Absorption  Pipette  (Townson  and  Mercer)        -  177 

24.  The  Flexible  Bellows-Pump  employed  by  Angus  Smith  to  draw 

out  Air  from  the  Air-Jar            .             .             -             -             -  181 

25.  Store  Bottle  for  Baryta  Water     -----  183 

26.  The  Apparatus  for  the  Lunge  and  Zeckendorf  Process     -             -  186 

27.  Haldane's  Apparatus  for  the  Estimation  of  CO2   -             -             -  188 

28.  Apparatus  for  collecting  the  Organic  Matter  in  Air          -             -  193 

29.  Showing  the  Characteristic  Disposition  of  the  Absorption  Bands 

in  the  Spectroscopic  Picture  of    Oxy-  and  Reduced  Haemo- 
globin    -  -  -  -  -  -  -  -198 


X  LIST   OF   ILLUSTRATIONS 

FIG.  I'AOK 

30.  The  Ozone  Cage  (Negretti  and  Zambra)  -             -             -             -  207 

31.  M.  Marie-Davy's  Modification  of  Pouchet's  Aeroscope     -             -  211 

32.  Hesse's  Apparatus  for  the  Collection  of  Suspended  Matters  in  Air  212 

33.  Hesse's  Apparatus  for  collecting  Ground  Air         -             -             .  219 

34.  The  Cream  Tube  (Townson  and  Mercer)  -             -             -             -  232 

35.  Stokes'   Tube   for  the   Werner-Schmidt  Process   (Townson  and 

Mercer)                .......  235 

36.  Centrifugal  Apparatus  for  Milk-Testing  -             -             -             -  238 

37.  Milk,  showing  the  Large  Colostrum  Corpuscles     -             -             -  240 

38.  Del6pine's  Milk-Collecting  Apparatus       .             -             .             -  251 

39.  Apparatus  for  the  Keichert-Wollny  Process        .             .             -  257 

40.  Aspergillus  glaucus              ......  263 

41.  Mucor  mucedo        .....--  264 

42.  The  Cheese  Mite  {Acarus  domesticus)        ....  264 

43.  The  Corn  Weevil  (Calandra  granaria)      ....  266 

44.  Vibriones  tritici    -               ......  266 

45.  A  Wheat  Spikelet  with  Ear-Cockle           ....  267 

46.  The  Wheat  Mite  {Acarus  farina)              ....  267 

47.  Ear  of  Rye  with  Ergot  (A),  and  a  Section  of  Ergot  (B)    -             -  267 

48.  Ergot         -             -             -             -             -             -             -             -  268 

49.  Smut  Spores  {Uredo  segetum)        .....  269 

50.  Bunt  {Uredo  fastida)           ......  269 

51.  Tilletia  caries  (Bunt)  and  Tilletia  IcBvis  -             -             ~             -  269 

52.  Puccinia  graminis  -  -  -  -  -  -270 

53.  Section  through  Branny  Envelope  and  Outer  Portion  of  Endo- 

sperm of  Wheat  Grain              -             -             -             -             -  270 

54.  Penicilliiim  glaucum          -_.._-  280 
Plates  V.  and  VI. — Illustrations  of  Starch  Grains          -  facing  286 

55.  Bruchus  Pisi  (of  the  Pea,  Bean,  etc.)      ....  288 

56.  Section  of  Wheat  Grain  (Outer  Coat)      ...             -  289 

57.  Wheat  Tissue  from  the  "  Testa  "  of  the  Grain    .             -             -  290 

58.  Barley  Tissue  from  the  "  Testa  "  of  the  Grain    -             .             -  290 

59.  Rye  Tissue  from  the  "  Testa  "  of  the  Grain        .             .             -  291 

60.  Oats  Tissue  from  the  "  Testa  "  of  the  Grain        .             .             _  291 

61.  Coccidium  oviforme  -  -  -  -  -  -297 

62.  Head  of  Tesnia  solium     -....-  299 

63.  Head  of  TcBnia  mediocanellata       -----  299 

64.  Brood  Capsule  of  an  Echinococcus            .             .             -             -  300 

65.  Trichina  spiralis,  encysted  in  Muscle         ....  301 

66.  One  of  Rainey's  Capsules             .....  303 

67.  Distoma  hepaticum             __...-  304 

68.  Apparatus   for  estimating  Fusel  Oil  by  Rose's  Process  (Baird 

and  Tatlock)      .--....  324 

69.  Torula  cerevisics  (Yeast  Plant)     ....             -  326 

70.  The  Cuticle  of  the  White  Mustard-Seed  -             -             -             -  336 

71.  Pepper       -             -             -             -             -             -             -             -  337 

72.  The  Sugar  Mite  {Acarus  sacchari)             -             .             .             .  339 

73.  Cofiec:  Cells  of  Testa  and  Cellular  Structure       -             -             -  3^5 


LIST   OF   ILLUSTRATIONS  XI 

FIG.  I'AGE 

74.  Chicory:  Dotted  Ducts  and  Cellular  Structure     -             -             -  34O 

75.  Lacteal  Vessels  of  Chicory             -             -             -             -             -  347 

76.  Cocoa  Starch  Cells             _.....  ^48 

77.  The  Elder  Leaf  (after  Bell)  -  -  -  -  -351 

78.  The  Willow  Leaf  (after  Bell)        -             -             -             -             -  351 

79.  The  Sloe  Leaf  (after  Bell)              .             _             .             .             .  ^52 

80.  The  Tea  Leaf  (after  Bell)             .....  ^52 

81.  The  Epidermis  of  the  Under  Surface  of  the  Tea  Leaf        -             -  353 

82.  Section  of  a  Tea  Leaf,  showing  Idioblasts             ...  ^53 

83.  Crystals  of  Arsenious  Acid            .             _             .             _             .  ^BS 

84.  Marsh's  Apparatus  for  Testing  for  Arsenic  (from  the  Analyst)    -  389 

85.  Arsenical  Mirrors  (W.  Thomson)  -             -             .             .             -  391 

86.  Delepine's  Apparatus  for  the  Oxidation  of  Arsenic  and  Sublima- 

tion of  Arsenious  Acid  from  Deposits  of  Arsenic  on  Copper     -  393 

87.  Apparatus  employed  in  the  Rideal-Walker  Method         -             -  408 


PLATE 


Paramaecmn 


NavLcida 


jEpii/tyd/xiJ.  CeUs 


Lepiolhnx 


_  A  FUamenlm  sheath 
'  B.    »   willwulshealh 


Cotton  Fibres. 


IyLn,en,J^ibres 


Miol  Fiire . 


Sa/c  Fibre. 


v  Foj-ticZe-  Cff/catfiej- 


Clalhrocyslis 


Aslenonella 


A^Uenrice  o/'jn^&ct^ 


OBJECTS   FOUND   IN    IMPURE   WATER  (VARIOUSLY   Magnified). 


PLATE  II. 


A  Tl^zier--  Bear 


J^ava,  cfJ^i^eci 


I'upa,  ofln^eci 


OBJECTS  FOUND      IN   IMPURE   WATER  (variously  Magnified). 


PLATE  III 


,^^A 


°im^ 


q/m 


Ad!yce^uufZ' 


FbwiaiUis 


Pollen. 


Spores  of Funffi 


A  Con/erroid  celi. 


Sacte/'Ucm,  iefmo. 


ADiatom' 


A  Ue-STmd 


Piffetailet  Spore 


^ 


Sitrireiia- 


Fun^z^ 


Jiil^i/  of  PJfiUry^lanfain 


frocococc-cu.  PUiMiali^ 


J^ella!  Lcb  fioccv^a. 


A  uqleri-a.  Vert  di^ 


CoTi/erva, 


ffoTTZpTioncTTia, 


OsaUaj-ia 


OBJECTS   FOUND  IN   IMPURE    WATER  (variously   Magnified). 


PLATE  IV. 


VoLvox  globator  1 1  Diiriu-gia 

Amirea  cochleans 


Stawashinn  crenulatum 


Spirogyra 


Egg  or  Q 

Dolhrwcephulus  Latas      0 

AnabsTicu 


CUosleruim  Diana; 


Egg  of 
Tapnia  Sohxum, 


Egg  of 
Ascaris  LunzbricohcLes 


Egg  of 
T  Medio  canellata 


Egg  of 


Egg  of 


Egg  of 


Tricocephalvis  Dbspar         Ankyloslomumdiwdenale  Oxinms  Vermiciilaris 


OBJECTS   FOUND   IN    IMPURE   WATER  (variously   Magnified). 


PUBLIC    HEALTH    LABORATORY 

WORK 

INTRODUCTORY  NOTES 

The  Collection  and  Weighing  of  a  Precipitate. 

The  substance  is  precipitated  from  a  known  bulk  of  liquid,  and 
the  precipitate  is  collected  on  a  filter-paper  which  has  been 
folded  and  placed  inside  a  glass  funnel.  The  filter  -  paper 
should  never  project  beyond  the  funnel,  and  the  fluid  should 
be  conducted  by  a  glass  rod  on  to  the  filter-paper,  to  prevent 
loss. 

Special  filter-papers  are  sold  which  yield  an  ash  which  is 
generally  quite  insignificant;  and  the  amount  of  ash  furnished 
by  them  is  a  definite  and  known  quantity  for  each  paper. 
Such  papers  should  be  always  employed  for  collecting  pre- 
cipitates which  have  subsequently  to  be  ignited  and  weighed. 

The  precipitate  on  the  filter-paper  is  next  washed  with  dis- 
tilled water  from  a  wash-bottle.  A  fine  jet  of  distilled  water, 
either  hot  or  cold,  is  generally  employed  for  this  purpose.  The 
process  of  washing  is  complete  if  a  drop  of  the  last  washing 
yields  no  residue  when  evaporated  on  a  platinum  spatula. 

The  precipitate  on  the  filter-paper  is  then  dried  in  a  drying- 
oven. 

Fig.  I  represents  Wills'  combined  water-bath  and  drying- 
oven.  It  consists  of  a  hot-water  bath  with  openings  for 
evaporating  dishes,  a  spacious  hot-air  chamber,  a  pair  of  hot- 
water  funnels  for  filtering  fatty  substances  which  tend  to  solidify 
when  cool,  and  a  hot-air  box  for  drying  test-tubes,  etc.  The 
thermometer,  in  situ,  registers  the  temperature  in  the  interior  of 
the  oven. 


2  LABORATORY  WORK 

The  filter-paper  should  then  be  folded  up,  placed  in  a  small 
porcelain  crucible  (previously  weighed),  and  covered  by  a  lid; 
the  filter-paper  and  precipitate  are  next  ignited  to  dull  redness, 
at  first  gently  so  as  to  obviate  spurting  and  loss,  but  the  lid 
should  be  removed  after  a  little  so  as  to  permit  free  access  of 
air.  It  is  also  desirable  to  keep  the  porcelain  dish  on  the  slant 
during  ignition,  since  this  favours  air  draught.  When  the  filter- 
paper  has  been  entirely  destroyed,  the  capsule  and  its  contents 
are  allowed  to  cool  under  a  desiccator,  and  weighed.  The  weight 
found,  minus  that  of  the  crucible  and  the  ash  of  tlie  filter-paper, 


FIG.    I. WILLS     WATER-BATH    AND    DRYING-OVEN. 


represents  the  weight  of  mineral  precipitate.  Care  must  be  taken 
to  remove  the  dish  from  the  flame  immediately  all  evidence  of 
charring  or  discoloration  has  disappeared,  and  not  to  conduct  the 
i  icineration  at  a  higher  temperature  than  is  found  absolutely 
necessary,  or  there  may  be  a  considerable  loss  in  the  mineral 
r3sidue.  Such  loss  is  most  generally  from  ammonia  salts  (by 
volatilization),  from  nitrates  and  nitrites  (by  loss  of  oxygen), 
frjm  certain  chlorides,  such  as  sodium  and  potassium  chlorides 
(by  volatilization),  from  combined  carbonic  acid,  and  from  the 


INTRODUCTORY    NOTES  3 

water  of  hydratcd  salts  (such  as  calcium  sulphate),  which  thercljy 
become  anhydrous. 

A  desiccator  is  simply  a  glass  shade  inside  of  which  there  is  a 
vessel  containing  some  agent  which  will  free  the  air  from  moisture 
(such  as  strong  sulphuric  acid  or  solid  calcium  chloride).  A 
residue  completely  dried  by  heat  will  absorb  a  little  of  the  vapour 
from  the  atmosphere  while  coohng  and  thus  increase  sHghtly  in 
weight,  unless  the  precaution  is  taken  to  place  it  inside  a  desic- 


^. 


FIG.    2. CHEMICAL    BALANCES. 


cator  during  the  coohng  process.  In  the  desiccator  a  perforated 
tray  or  a  tripod  supports  the  substance  to  be  cooled,  and  the 
rim  against  which  the  cover  closely  fits  is  greased  with  tallow  so 
that  the  desiccator  is  hermetically  sealed. 

The  balances  shown  in  Fig.  2  will  be  found  to  be  suitable  to 
all  weighing  purposes.  They  consist  of  a  short  beam  which 
supports  two  pans,  the  ends  of  the  beam  being  constructed  with 
straight  knife-edges  of  agate,  upon  which  the  pans  are  suspended 
by  agate  planes.     The  case  is  fitted  with  a  sHding  window  in 


4  LABORATORY   WORK 

front,  which,  even  when  closed,  admits  of  the  working  of  the 
scales  by  means  of  turning  a  screw  which  projects  externally. 
The  balances  must  be  kept  in  a  dry  room,  away  from  any 
fireplace  or  door,  and  placed  on  a  perfectly  firm  and  level 
surface. 

The  operation  of  weighing  consists  of  first  lifting  the  beam  off 
its  support  by  turning  the  screw,  and  then  noting,  by  the  long 
indicator  which  hangs  down  in  front  of  the  central  vertical 
support  of  the  balances,  whether  the  two  pans  exactly  counter- 
balance each  other;  if  not,  the  balance  must  be  adjusted  by 
means  of  a  small  mechanism  situated  on  the  top  of  the  centre  of 
the  cross-beam,  which  can  be  moved  to  the  right  or  left,  accord- 
ing as  it  is  necessary  to  increase  the  weight  in  either  of  these 
diiections. 

After  thus  seeing  that  the  scales  are  accurately  equipoised, 
the  material  is  then  placed  upon  one  of  the  trays,  and  the 
weights  are  added  to  the  other. 

After  each  alteration  made  in  the  weights,  the  result  must,  of 
course,  be  tested;  and  before  any  further  addition  or  removal  is 
made  the  scales  must  be  brought  to  rest  upon  their  supports,  or 
the  apparatus  may  be  put  out  of  gear. 

Each  of  the  weights  is  marked.  The  larger  brass  weights 
(i  to  50)  represent  grammes,  the  next  in  size  decigrammes 
(o-i  to  0-5),  the  next  centigrammes  (o-oi  to  0-05);  and  small 
forceps  are  used  for  picking  up  and  applying  them  to  the  pan. 
The  milligrammes  are  added  by  a  little  piece  of  bent  wire  (the 
"  rider  "),  which  is  carried  by  means  of  a  shding-rod  moving  just 
above  the  level  of  the  cross-beam,  which  beam  bears  markings 
numbered  from  i  to  10.  By  sliding  the  rod,  the  "  rider  "  may 
be  carried  to,  and  placed  upon,  an}^  one  of  these  marks,  when 
that  number  of  milligrammes  of  weight  will  have  been  added. 
Each  milligramme  division  is  further  subdivided  to  i  parts  of  a 
milligramme. 

Example. — A  small  platinum  dish  is  placed  on  the  left-hand 
pan. 

A  5-gramme  weight  is  placed  on  the  other  pan. 

The  beam  is  raised  by  means  of  a  half-turn  of  the  screw; 
when    the    platinum    dish    is    found    to    be    heavier    than    the 

5  grammes. 

The  scales  are  put  at  rest  by  reversing  the  screw  to  its  original 
position,  and  a  2-gramme  weight  is  added  to  the  5.     This  is 


INTRODUCTORY    NOTES  5 

also  carried  up  by  the  greater  weight  of  the  platinum  dish. 
Another  gramme  is  added;  and  being  found  to  be  too  much,  is 
removed.     The  dish  therefore  weighs  between  7  and  8  grammes. 

A  5-decigramme  weight  {i.e.,  0-5  gramme)  is  added.  The 
platinum  dish  is  still  slightly  the  heavier ;  therefore  another  deci- 
gramme is  added,  with  the  result  that  the  weights  now  slightly 
overbalance  the  dish.  The  i-decigramme  weight  is  removed. 
The  dish  therefore  weighs  7-5  grammes,  but  not  7-6  grammes. 

A  5-centigramme  weight  (0-05)  is  added.  This  is  not  enough; 
but  a  3-centigramme  weight  further  added  so  extremely  nearly 
establishes  the  required  equihbrium  that  the  addition  of  another 
centigramme  is  found  to  be  too  much.  Therefore  the  dish 
weighs  7-57  grammes,  but  not  7-58  grammes. 

Three  milhgrammes,   added  by  means  of  the  little  "  rider,' 
make  the  long  indicator  oscillate  quite  evenly  on  either  side  of 
the  central  mark  on  the  piece  of  porcelain,  where  it  would  ulti- 
mately come  to  rest. 

The  weight,  therefore,  of  the  platinum  dish  is : 

7  grammes  =     7 

5  decigrammes  =     0-5 

7  centigrammes  =0-07 

3  milligrammes  =     0-003 


Total  =     7 '573  grammes. 

The  dish  need  not  be  reweighed  on  every  occasio-n  of  using  if 
it  is  thoroughly  cleansed;  the  reweighing  is  only  necessary  at 
intervals  of  every  few  days. 


The  Collection  and  Weighing  of  a  Solid  Residue 
AND  Mineral  Ash. 

A  given  weight  of  the  liquid  is  placed  in  a  clean  weighed 
platinum  dish.  (A  platinum  dish  is  cleansed  after  use  with  a 
little  dilute  hydrochloric  acid;  then  well  washed  in  pure  water; 
and  finally  heated  to  redness  in  the  Bunsen  flame.  It  should  be 
allowed  to  cool  under  the  desiccator  prior  to  weighing.)  The 
dish  and  its  contents  are  then  placed  upon  a  water-bath. 

A  water-bath  is  a  receptacle  which  holds  water,  and  admits 
of  this  water  being  heated  to  a  certain  temperature.  When 
vessels  containing  liquids  are  made  to  stand  over  the  heated 
water,  evaporation  of  their  fluid  contents  may  be  effected  at  a 


O  LABORATORY   WORK 

temperature  which  can  never  quite  reach  that  of  the  boiling-point 
of  water. 

The  water-bath  must  not  be  allowed  to  boil  dry.  Fig.  3  shows 
an  arrangement  by  which  this  may  be  guarded  against,  by  the 
maintenance  of  a  constant  water-level  in  the  bath. 

When  the  contents  of  the  dish  have  evaporated  to  dryness, 
the  dish  is  placed  in  the  desiccator  for  half  an  hour  to  cool.  It 
is  then  weighed,  and  the  solid  residue  is  the  weight  obtained  less 
the  weight  of  the  platinum  dish. 

The  dish  is  then  held  by  a  pair  of  crucible  tongs  (which  may, 
with  advantage,  be  platinum-pointed)  in  the  flame  of  a  Bunsen 


FIG.    3. WATER-BATH    WITH    CONSTANT    WATER-LEVEL. 

burner,  until  nothing  but  the  mineral  ash  remains.  Fletcher's 
burners  are  an  improvement  upon  the  common  type  of  Bunsen 
burner,  when  it  is  required  to  employ  a  very  small  flame. 

The  mineral  ash  is  allowed  to  cool  in  the  desiccator  and  then 
weighed. 

Specific  Gravity  or  Relative  Density. 

The  relative  density  or  specific  gravity  of  a  solid  or  hquid  is 
generalty  referred  to  water,  taken  as  unity  or  as  a  thousand. 
Where  possible,  the  test  must  be  applied  at  the  temperature  of 
15-5°  C. ;  but  in  the  case  of  fats  a  higher  temperature  is  necessary 
in  order  to  obtain  them  in  a  liquid  state. 

The  student  is  already  famihar  with  the  float  instruments  or 
hydrometers  which  are  commonly  in  use  for  obtaining  specific 
gravities,  and  it  is  only  necessary  to  point  out  the  importance 
of  verifying  all  these  instruments  prior  to  use,  by  comparing  their 
indications  with  the  results  obtained  by  more  delicate  methods. 

The  most  accurate  estimates  of  specific  gravity  are  obtained 
by  actual  weighings  in  the  specific  gravit}^  bottle.  The  method 
may  be  illustrated  by  indicating  how  the  specific  gravity  of 
butter-fat  would  thus  be  obtained. 


INTRODUCTORY    NOTES  7 

1.  A  quantity  of  the  butter  is  heated  to,  and  maintained  at 
about  65°  C.  in  a  water-bath  made  by  standing  a  small  beaker 
containing  the  butter  in  a  larger  beaker  containing  water. 

2.  The  fat  slowly  separates  and  forms  an  upper  stratum, 
which  rests  upon  a  lower  stratum  of  the  water,  curd  and 
salt. 

3.  In  the  course  of  time  the  upper  layer  of  butter-fat  gets 
clearer  and  clearer,  until  at  last,  all  the  water,  curd,  and  salt 
having  separated,  it  becomes  clear  and  transparent.  Immedi- 
ately this  has  taken  place  the  fat  is  decanted  on  to  a  fine  dry  filter, 
in  order  to  guard  against  the  presence  of  traces  of  curd  and  salt ; 
and  the  filtrate  of  pure  butter-fat  is  collected  and  poured  into  a 
specific  gravity  bottle.  The  specific  gravity  bottle  is  a  small 
vessel  of  thin  glass,  fitted  with  a  thermometer  which  also  forms  a 


FIG.    4. A    SPECIFIC    GRAVITY    FLASK. 

stopper  to  the  bottle  and  which  registers  the  temperature  of  the 
contained  liquid,  so  that  this  may  be  known  at  the  moment  of 
weighing.  This  bottle  must  be  accurately  filled  and  then 
stoppered,  care  being  taken  that  no  air-bubble  or  empty  space 
is  allowed  to  remain  between  the  stopper  and  the  liquid. 

4.  The  temperature  at  which  the  fat  is  poured  into  the  specific 
gravity  bottle  should  be  a  fraction  above  38°  C,  when  the  bottle 
and  its  contents  are  transferred  to  the  balance  and  weighed. 

The  precise  weight  must  be  taken  when  the  thermometer 
registers  exactly  38°  C,  the  flask  is  entirely  filled  with  the  fat, 
and  there  is  no  evidence  of  air-bubbles. 

The  weight  of  the  specific  gravity  bottle  when  completely  filled 
with  distilled  water  and  closely  stoppered  at  the  temperature  of 
38°  C,  has  been  previously  taken.     By  a  comparison  of  the  respec- 


8 


LABORATORY   WORK 


live  weights  of  the  two  fluids  when  occupying  the  flask  at  the 
same  temperature,  the  specific  gravity'  of  the  butter-fat  is 
obtained,  that  of  distilled  water  being  taken  as  i,ooo — 


i.e.,  S.G.= 


The  weight  of  the  fat  at  38°  C. 
The  weight  of  the  water  at  38°  C. 


X  1,000. 


38°  C.  is  here  selected  as  the  temperature  for  weighing  because 
it  is  the  lowest  temperature  to  which  it  is  quite  safe  to  reduce 


FIG.    5. THE    WESTPHAL    BALANCE. 

the  contents  of  the  bottle  without  any  solidification  ensuing, 
all  the  fats  (animal  and  vegetable)  used  as  adulterants  of  butter 
remaining  hquid  at  that  temperature. 

The  Westphal  balance  registers  the  specific  gravity  on  the 
principle  that  a  body  immersed  in  a  liquid  loses  a  part  of  its 
weight  which  is  equivalent  to  the  weight  of  the  displaced  liquid. 
The  apparatus  (Fig.  5)  has  a  swinging  arm,  which  rests  on  a 
knife-edge,  and  the  upper  surface  of  a  part  of  the  arm  is  notched 
and  graduated.  At  the  free  end  of  the  graduated  part  of  the 
arm  is  a  hook,  by  which  a  glass  plummet  is  suspended  by  means 
of  fine  platinum  wire.  Three  different-sized  riders  (or  weights) 
are  provided,  of  which  the  largest  indicates  hundreds,  the  next 


INTRODUCTORY    NOTES  9 

tens,  and  the  smallest  units.  At  the  other  end  of  the  arm  is  a 
metal  pointer,  and  the  balance  prior  to  use  must  be  so  adjusted 
that,  with  the  plummet  immersed  in  distilled  water,  and  the 
largest  rider  placed  on  the  hook  (which  represents  the  tenth 
notch,  or  i,ooo),  this  pointer  rests  vertically  opposite  a  small 
projection  on  the  frame.  The  adjustment  is  made  by  means 
of  the  small  screw  shown  on  the  vertical  support  to  the  frame. 
The  liquid  is  placed  in  a  glass  cylinder  and  the  plummet  just 
completely  immersed  in  the  hquid,  and  by  placing  the  riders  on 
various  notches  the  two  pointers  are  again  brought  opposite  to 
each  other.  If,  for  instance,  in  order  to  obtain  this  result,  the 
largest  rider  is  on  the  ninth  notch,  the  next  largest  on  the 
seventh,  and  the  smallest  on  the  fifth,  the  specific  gravity  would 
be  975. 

A  correction  for  temperature  is  necessary  for  an  exact  observa- 
tion by  float  hydrometers,  since  all  such  instruments  are  originally 
graduated  by  water  at  the  temperature  of  i5'5°  C,  and  the 
specific  gravity  varies  with  the  temperature.  Within  the  ordinary 
ranges  of  temperature  in  a  laboratory  it  is  sufficient  to  add  1°  of 
specific  gravity  for  every  3°  of  temperature  above  i5'5°  C,  and 
to  subtract  1°  for  every  3°  below  I5"5°  C. 

The  Extraction  of  Fat  by  Soxhlet's  Apparatus. 

Soxhlet's  apparatus  is  shown  in  Fig.  6.  A  is  the  small  flask 
which  has  been  thoroughly  dried  and  weighed  and  then  about 
half  filled  with  ether ;  the  extraction  apparatus  is  shown  attached 
to  the  flask  between  it  and  the  condenser  (K),  the  latter  being 
fixed  in  a  very  slanting  position.  F  represents  a  piece  of  fat- 
freed  paper  containing  the  substance  to  be  extracted;  this  is 
placed  in  D,  care  being  taken  that  it  is  entirely  below  the  level 
of  the  smiall  siphon  E,  so  that  it  may  be  completely  immersed 
in  the  solvent,  and  also  that  it  does  not  close  the  opening  to  the 
siphon. 

The  weighed  flask  of  the  Soxhlet  should  have  a  capacity  of 
about  150  c.c,  and  contain  about  75  c.c.  of  ether. 

The  dish  on  which  the  flask  stands  is  partially  filled  with  water, 
and  this  is  cautiously  heated;  the  ether  vapour  then  ascends  G, 
passes  into  the  condenser,  and  is  at  once  condensed  and  drops 
on  to  F;  the  ether  goes  on  accumulating,  rising  the  while  in  the 
ascending  arm  of  E,  until  it  reaches  the  level  of  the  upper  bend. 


10 


LABORATORY   WORK 


and  overflows,  when  siphonage  takes  place,  and  the  ether  passes 
out  of  D  back  to  the  flask.  Thus  the  circulation  of  the  ether  is 
completed  every  few  minutes.  Immediately  after  a  siphon  dis- 
charge has  returned  all  the  ether  to  the  flask,  the  latter  is 
removed,  the  ether  driven  off  over  the  water-bath  at  a  temper:  - 
ture  sufficient  to  make  the  ether  boil,  after  which  the  flask  and  its 
contents  are  dried  at  ioo°  C.  until  a  constant  weight  is  obtained. 
Of  course,  there  must  be  no  doubt  as  to  whether  the  extrac- 
tion has  been  complete;  this  may  be  tested  by  fixing  a  second 


FIG.  6. — soxhlet's  fat-extraction  apparatus. 


small  flask  containing  more  ether,  and  after  about  half  an  hour 
evaporating  off  the  ether  and  drying  at  ioo°  C. ;  it  can  then  be 
noted  whether  there  is  any  material  increase  over  the  original 
weight  of  the  flask. 

It  is  well  to  place  a  small  plug  of  blotting-paper  in  the  mouth 
of  the  open  tube  at  the  top  of  the  condenser  so  as  to  limit  the 
access  of  air,  the  moisture  of  which  would  otherwise  condense 
and  slightly  wet  the  ether. 


INTRODUCTORY    NOTES 


II 


The  vSpectroscope. 

A  knowledge  of  the  spectroscope  is  useful  to  the  public  health 
worker,  and  for  those  unacquainted  with  the  use  of  this  instru- 
ment a  brief  description  is  given: 

If  a  compound  light,  such  as  sunlight,  is  made  to  pass  through 
a  glass  prism,  the  different  coloured  rays  of  which  it  consists  are 
unequally  refracted  (or  bent  out  of  their  original  course),  so  that 
beyond  the  prism  they  form,  upon  a  white  surface,  a  continuous 
line  of  colours  called  the  "  spectrum  ";  and  the  spectrum  of  the 
compound  white  light  will  be  seen  to  consist,  in  order  from  right 
to  left,  of  red,  orange,  yellow,  green,  blue,  indigo,  and  violet.  A 
number  of  dark  hues — called  "  absorption  bands  "  or  "  Fraun- 
hofer's  hues  " — are  also  seen  to  cross  the  image  of  the  solar 


FIG.    7.— THE    SPECTROSCOPE. 


spectrum.  These  lines  indicate  the  absence  of  raj^s  of  certain 
refrangibilities  from  the  beam  of  solar  hght;  each  occupies  a 
definite  position,  and  therefore  affords  a  means  of  accurately 
localizing  the  parts  of  the  spectrum. 

In  other  lights  the  spectrum  will  only  show  a  few  bright  bands 
(that  of  the  sodium  flame  only  one),  and  the  remainder  of  the 
spectral  image  is  almost — or  quite — invisible,  by  comparison. 

If  we  transmit  solar  light  through  different  coloured  solutions, 
we  then  get  different  absorption  bands.  If  a  solution  of  fresh 
blood,  for  instance,  be  taken,  and  a  small  colourless  cell  containing 
it  is  placed  before  the  slit  in  the  instrument  which  admits  the 
hght,  two  distinct  and  characteristic  dark  stripes  or  absorption 
bands  appear  in  the  yellow  and  green  parts  of  the  solar  spectrum. 


12  LABORATORY  WORK 

Fig.  7  will  serve  to  show  the  manner  in  which  a  spectroscope 
is  constructed. 

A  firm  iron  stand  is  seen  to  support  at  its  upper  end  a  brass 
plate  carrjing  the  glass  prism;  laterally,  a  cjdinder  is  also 
fastened  to  the  brass  plate,  and  in  the  end  of  this  cylinder  which 
is  nearest  the  prism  a  lens  is  placed,  the  other  end  being  closed 
by  a  plate  with  a  vertical  slit  in  it  (the  width  of  which  can  be 
regulated  by  a  screw  to  meet  requirements) ;  through  this  slit  the 
light  is  admitted  to  the  prism,  the  rays  first  passing  through  the 
lens  and  thereby  being  rendered  parallel  and  condensed.  The 
spectroscopic  appearance  is  then  viewed  through  a  small  tele- 
scope (with  a  low  magnifying  power),  and  this  (the  tube  on  the 
right  as  seen  in  the  figure)  is  fitted  on  to  the  cast-iron  foot  so  as 
to  be  movable  in  a  horizontal  plane  about  the  axis  of  the  foot. 
The  telescope  is  made  to  move  over  a  scale  which  can  be  read 
^^^th  a  vernier. 

All  foreign  light  must,  of  course,  be  cut  off;  and  this  may  be 
done  by  a  black  cloth,  which  is  thrown  over  the  prism  and  the 
tubes. 

The  sht  may  be  furnished  with  a  reflecting  prism,  by  means  of 
which  two  spectra  can  be  compared  at  the  same  time. 

Thus,  by  a  spectroscopic  examination,  the  colour,  number, 
and  position  of  the  bright  lines  on  the  spectroscopic  scale  may 
be  carefully  observed  and  noted.  If  it  is  desired  to  distinguish 
metals  by  means  of  their  spectral  lines,  the  substance  is  dissolved 
in  a  drop  of  the  purest  hydrochloric  acid;  a  piece  of  recentty 
ignited  platinum  wire  is  then  dipped  in  the  solution  and  held  in 
a  Bunsen  flame. 

A  convenient  method  of  performing  spectroscopic  observations 
is  by  means  of  the  Sorby- Browning  micro-spectroscope,  which 
consists  of  a  small  spectroscope  placed  in  connection  with  a 
microscope  in  such  a  way  that  the  former  fits  into  the  tube  of 
the  latter,  similar  to  an  eyepiece. 

The  Polariscope. 

A  simple  form  of  half-shadow  polariscope  consists  of  a  hori- 
zontal brass  tube  mounted  on  a  vertical  stand,  and  having  a 
Nicol  prism  at  each  end,  one  being  the  "  polarizer,"  and  the 
other  the  "  analyzer."  A  monochromatic  hght,  such  as  the 
yellow  sodium   flame   (which  may  be  obtained  by   placing   a 


INTRODUCTORY    NOTES  13 

platinum  cup  containing  sodium  chloride  in  the  flame  of  a  Bunsen 
burner)  is  admitted  to  the  polarizer.  At  the  opposite  end  of  the 
brass  tube  an  eyepiece  is  fitted  just  in  front  of  the  analyzer. 
In  the  brass  tube  can  be  placed  a  clean  and  dry  glass  tube  con- 
taining the  solution  under  examination. 

Light  consists  of  vibrations  of  ether  in  all  planes,  and  its  trans- 
mission occurs  in  waves;  but  the  monochromatic  light  consists 
of  light  of  a  single  wave-length.  The  polarizer  allows  only  the 
vibrations  taking  place  in  one  plane  to  pass,  others  being  inter- 
cepted. Now,  when  the  analyzer  is  placed  parallel  to  the  polar- 
izer, all  the  vibrations  pass  through  the  analyzer  also,  and  equal 
illumination  is  seen  on  both  sides  of  a  sharply  defined  vertical 
middle  hne  when  looking  through  the  eyepiece,  this  point  of 


FIG     8. THE    POLARISCOPE. 

equal  illumination  being  called  the  "  zero-point."  The  slightest 
rotation  of  the  analyzer  will  then  produce  a  difference  in  the 
illumination  of  the  two  sides. 

In  using  the  instrument,  the  zero-point  is  first  obtained,  with 
the  glass  observing-tube  filled  with  distilled  water  and  placed  in 
position;  then  if  some  sugar  solution  (or  other  optically  active 
liquid,  which  has  the  property  of  rotating  the  plane  of  polarized 
light)  be  placed  in  the  glass  tube,  the  rays  will  no  longer  pass 
through  the  analyzer,  and  the  equal  illumination  is  disturbed. 
If  the  analyzer  be  turned  round,  it  is  possible  to  obtain  an  equal 
illumination,  or,  in  other  words,  to  compensate  for  the  optical 
disturbance  of  the  rotating  substance;  but  the  direction  and  the 
angle  through  which  it  has  been  turned  (as  indicated  on  a  dial 
fitted  with  a  vernier)  vary  with  the  amount  and  nature  of  the 
rotating  substance  examined,  the  number  of  degrees  being  termed 


14  LABORATORY   WORK 

the  "  index  of  refraction,"  from  which  the  so-called  "  specific 
rotary  power  "  of  the  substance  may  be  calculated. 

The  polariscope  is  used  to  find  the  percentage  adulteration  of 
butter  with  other  fats  (refractometer),  and  also  the  strength 
of  saccharine  solutions  (saccharimeter).  With  pure  butter  an 
equally  distributed  light  can  be  obtained,  but  with  butter  con- 
taining fat  which  has  been  melted  (margarine)  this  is  impossible, 
since  such  fats  rotate  the  plane  of  polarization.  Glucose  in 
honey  and  added  sugar  to  milk  may  also  be  detected  by  this 
instrument,  for  while  most  sugars  have  the  property  of  deflecting 
the  ray  of  polarized  light  to  the  right  (dextro-rotary,  indicated 
by  the  sign  +),  others  deflect  to  the  left  (levo-rotary,  indicated 
by  the  sign  — ),  and  this  affords  a  means  of  distinguishing 
between  them.  If  the  nature  of  the  substance  is  known,  one 
can,  moreover,  estimate  its  quantity,  since  i  gramme  of  a 
particular  optically  active  substance  has  its  own  specific  rotary 
power. 

But  for  the  work  demanded  of  the  public  health  worker  it  is 
not  necessary  to  determine  specific  rotary  powers,  useful  as  these 
may  be  in  some  of  the  work  which  a  public  analyst  may  be 
called  upon  to  perform.  Indeed,  from  the  standpoint  of  the 
public  health  worker  the  micro-polariscope  (in  which  the  polari- 
scope is  adjusted  to  an  ordinary  microscope)  will  generally 
suffice.  In  this  instrument  one  of  the  Nicol  prisms  (the 
analyzer)  is  inserted  in  the  brass  tube  of  the  microscope  imme- 
diately above  the  objective,  and  the  other  (the  polarizer)  is  fitted 
beneath  the  stage  of  the  microscope,  so  that  the  specimen 
examined  on  the  slide  stage  of  the  microscope  is  now  between 
two  Nicol  prisms,  the  lower  one  of  which  is  the  polarizer.  Such 
an  instrument  will  be  found  of  assistance  in  distinguishing 
between  certain  starches,  some  of  which  polarize  better  than 
others,  in  detecting  the  addition  of  starchy  matter  (such  as  rice) 
to  pepper  or  mustard  (which  do  not  polarize  in  the  mass),  and  in 
distinguishing  between  pure  butter  and  margarine.  When,  for 
instance,  a  specimen  of  pure  pepper  is  examined,  it  is  possible  to 
obtain,  by  rotating  the  analyzer,  a  completely  darkened  field; 
whereas  this  is  impossible  when  ground  rice  is  the  article  under 
examination.  Hence  the  addition  of  ground  rice  to  pepper  can 
readily  be  detected  from  the  circumstance  that  it  is  not  possible 
to  obtain  a  completely  obscured  field.  Similarly,  with  pure 
butter  a  completely  dark  field  cannot  be  obtained,  whereas  with 


INTRODUCTORY   NOTES 


15 


margarine  from  fat  which  has  been  melted  it  can;  and  in  the 
case  of  mixtures  it  is  impossible  to  completely  obscurr;  tiio  field 
by  rotating  the  analyzer. 

Graduated  Burettes. 
In  working  with  delicate  standard  solutions  it  is  best  to 
employ  a  mounted  burette  fitted  with  a  stopcock  at  the  bottom, 
rather  than  an  unmounted  one  controlled  by  the  finger;  as  in  the 
former  case  the  possibihties  of  contamination  are  reduced,  and 
there  is  no  risk  of  any  loss  from  the  burette  while  the  operator 
is  mixing  or  colour-matching  in  the  intervals  of  the  addition 
of  further  quantities  of  the  standard  solution.  When  a  hand- 
burette  is  employed  the  index-finger  which  controls  its  delivery 
must  be  quite  dry. 


Its: 

10 
9 

FIG.    9. A    BURETTE    FILLED    UP    TO    THE    lO    C.C.    MARK. 

Unmounted  burettes  should  not  be  blown  out,  but  allowed  to 
drain,  and  the  drop  at  the  dehvery  end  removed  by  touching  the 
side  of  the  vessel  into  which  the  contents  are  emptied. 

In  judging  the  height  to  which  fluid  stands  in  a  burette, 
always  take  the  level  of  the  convex  lower  border  of  the  meniscus 
which  forms  upon  its  upper  surface,  and  make  this  rest  upon  the 
Hne  to  which  the  fluid  is  required  to  reach.  Water  standing  to 
the  level  of  10  c.c.  in  a  burette  will  appear,  therefore,  as  in  Fig.  9. 
The  eye  must  always  be  on  a  level  with  the  upper  surface  of  the 
liquid  when  a  reading  is  made. 

The  burette  just  holds  10  c.c.  of  water  if  at  a  temperature  of 
about  15°  C.  the  water  weighs  9-99  grammes.  Similarly,  with  a 
100  c.c.  measuring  flask  the  graduation  is  correct  if  the  100  c.c. 
of  water,  at  about  15°  C,  weigh  99-9  grammes. 


i6 


LABORAtORY  WORK 


For  cleaning  glass  burettes,  etc.,  and  porcelain  apparatus, 
especially  from  fatty  matter,  the  commercial  trisodium  phosphate 
is  useful. 

International  Atomic  Weights  (1914).     0=i6. 

Aluminium 

Arsenic 

Barium 

Boron 

Bromine 

Calcium 

Carbon 

Chlorine 

Chromium 

Copper 

Fluorine 

Hydrogen 

Iodine 

Iron 

Lead 

Magnesium 

Manganese 

Mercury 

Nitrogen 

Oxygen 

Phosphorus 

Potassium 

Silicon 

Silver 

Sodium 

Sulphur 

Tm 

Zinc 


(Al) 

= 

27-1 

(As) 

= 

74-96 

(Ba) 

= 

137-37 

(B) 

= 

II'OO 

(Br) 

= 

79-92 

(Ca) 

= 

40-07 

(C) 

= 

I2-00 

(CI) 

= 

35-46 

(Cr) 

= 

52-00 

(Cu) 

= 

63-57 

(Fl) 

= 

19-00 

(H) 

= 

1-008 

(I) 

= 

126-92 

(Fe) 

= 

55-84 

(Pb) 

= 

207-10 

(Mg) 

= 

24-32 

(Mn) 

= 

54-93 

(Hg) 

= 

200-60 

(N) 

= 

14-01 

(O) 

= 

i6-oo 

(P) 

= 

31-04 

(K) 

= 

39-10 

(Si) 

— 

28-30 

(Ag) 

= 

107-88 

(Na) 

= 

23-00 

(S) 

^ 

32-07 

(Sn) 

= 

119-00 

(Zn) 

= 

65-37 

Weights  and  Measures  upon  the  j\Ietrical  System. 

The  metrical  system  is  founded  upon  the  "  metre,"  which  is 
divided  or  multiplied  by  ten  to  represent  different  measures,  as 
follows : 

Length. 

inVu  part  of  a  metre, 
ji-  part  of  a  metre. 
jV  part  of  a  metre. 


I  millimetre 
I  centimetre 
I  decimetre 
I  metre 
I  decametre 
I  hectometre 
I  kilometre* 


39-37  inches. 
10  metres. 
100  metres. 
1,000  metres. 


*  The  Latin  prefix  therefore  indicates  division,  the  Greek  multiplication. 


INTRODUCTORY    NOTES 


Capacity. 

I  cubic  centimetre 
28'35  cubic  centimetres 
1,000    cubic    centimetres 

or  I  cubic  decimetre 
I  litre  =  35-3  ounces 
I  pint 
1,000  litres 


O'oGi  cubic  inch. 
I  fluid  ounce. 

I  litre. 

1-765  pints. 

568  cubic  centimetres, 

1  cubic  metre. 


17 


One  c.c.  of  distilled  water  at  4°  C,  and  760  millimetres  baro- 
metric pressure,  weighs  i  gramme,  which  is  the  standard  of  weight. 


Weight. 


I  milligramme  = 

I  centigramme  = 

I  decigramme  = 

I  gramme  = 

I  decagramme  = 

I  hectogramme  = 

I  kilogramme  = 

I  ounce  = 
I  pound  (16  ounces)    = 

I  gallon  of  water  = 

I    litre   of   hydrogen   at   0°   C,  and 

O'oSgS  gramme. 

I    litre    of    oxygen    at    0°    C,  and 

O'oSqGx  16  grammes. 


tttVo  part  of  a  gramme. 

jItj  part  of  a  gramme. 

^^  part  of  a  gramme. 

15-432  grains. 

10  grammes. 

100  grammes. 

1,000  grammes. 

28-35  grammes  =  437-5  grains. 

453*6  grammes  =7,000  grains. 

4-536  litres  =  10  pounds. 

760   millimetres    pressure,   weighs 
760    millimetres    pressure,    weighs 


Thermometer  Scales. 


Centigrade. 

Reaumur 

Fahrenheit 


Freezing-point  =      o 


3- 


Boiling  point  =100 


Centigrade     Reaumur     Fahrenheit  —  32 


5  4  9  ■ 

To  convert  Centigrade  to  Fahrenheit,  x  9-^5,  and  add  32. 
Fahrenheit  to  Centigrade,  subtract  32,  -=-9x5. 
Reamur  to  Fahrenheit,  -f  4  x  9,  and  add  32. 
grains  to  grammes,  x  0-0648. 
cubic  feet  to  cubic  metres,  x  0-0283. 
cubic  feet  to  litres,  x  28-3. 


PART    I 

THE  CHEMICAL,  MICROSCOPICAL,  AND 

PHYSICAL    EXAMINATION    OF    WATER    FOR 

PUBLIC  HEALTH  PURPOSES 

CHAPTER  I 

THE  COLLECTION  OF  SAMPLES— INFORMATION  REQUIRED 
AS  TO  SAMPLES— QUANTITATIVE  EXPRESSIONS 

The  sample  should  always  be  collected  for  analysis  just  as  it  is 
ordinarily  obtained  for  drinking  purposes.  It  is  obvious,  since 
our  object  is  to  discover  all  the  possibilities  of  danger,  that  an 
endeavour  should  be  made  to  ascertain  the  maximum  amount  of 
pollution  to  which  the  water  is  liable.  For  instance,  in  the  case  of 
streams,  lakes,  etc.,  the  point  of  entrance  of  any  drains,  should 
only  be  avoided  to  the  same  extent  as  it  is  by  those  who  may 
come  to  collect  their  drinking-water. 

When  there  is  a  general  system  of  water-supply,  an  effort  must 
be  made  to  meet  the  same  ends  by  choosing  samples  from  the 
street  fountains  and  street  mains,  rather  than  from  storage,  etc., 
reservoirs.  But  since  impurities  may  gain  access  during  domestic 
storage  and  distribution,  it  would  not  be  fair  in  all  cases  to  judge 
a  public  supply  from  the  tap-water  of  any  particular  dwelling. 

With  regard  to  shallow  wells  from  which  the  water  is  removed 
by  pumping,  it  is  advisable  to  continue  the  process  for  some  time, 
but  no  longer  than  it  is  judged  that  the  water  may  be  pumped 
during  any  one  day,  under  the  prevailing  circumstances  of 
demand.  This  is  done  because  the  last  "  pumpings  "  will  often 
furnish  the  maximum  evidence  of  any  pollution  present. 

To  ascertain  whether  the  water  may  have  been  contaminated 
during  its  domestic  storage  and  distribution,  the  sample  should 
be  taken  from  the  lowest  draw-off  tap  (gener  ally  the  scullery  sink 

19 


20  LABORATORY  WORK 

tap),  as  then  the  water  will  have  run  the  maximum  risk  of 
contamination. 

When  the  fact  is  borne  in  mind  that  the  water  from  many 
shallow  wells  is  materially  influenced  both  as  to  quantity  and 
quality  by  the  rainfall,  it  will  be  understood  how  samples  from 
the  same  well  may  vary  in  purity  according  as  to  whether  a  long 
dry  period  may  have  preceded  the  collection,  or  a  heavy  rainfall, 
which  may  be  the  means  of  conveying  to  the  well,  water  impreg- 
nated with  surface  washings,  or  water  which  may  have  washed 
accumulated  impurities  out  of  the  interstices  of  the  soil.  These 
facts  as  to  rainfall  should  always  be  ascertained ;  and  it  may  be 
desirable  to  examine  a  further  sample  after  prolonged  and  heavy 
rain. 

The  fact  as  to  whether  a  cesspool  or  drain  contaminates  a  well 
can  readily  be  decided  either  by  introducing  a  considerable 
quantity  of  sodium  chloride,  followed  by  plenty  of  water,  and 
estimating  the  chlorine  in  the  well-water  every  morning  and 
evening  for  several  days;  or  by  introducing  a  strongly  alkaline 
solution  of  fluorescine,  and  endeavouring  to  detect  the  green 
colour  in  the  well-water. 

Water  is  customarily  collected  for  analysis  in  a  large  glass- 
stoppered  bottle,  called  a  "  Winchester  quart,"  which  holds  about 
twice  the  amount  which  is  implied  by  its  description  {i.e.,  about 
half  a  gallon).  Stout  wicker  covers  are  made  to  protect  them  in 
transit  by  parcel  post  or  rail.  These  bottles  have  become  gener- 
ally adopted  because,  in  addition  to  holding  an  amount  which 
meets  all  the  requirements  of  an  ordinary  analysis  (even  though 
it  be  necessary  to  repeat  some  of  the  estimations),  they  are 
strongly  made;  but  obviously  any  stout  glass  bottle  of  similar 
dimensions,  fitted  with  a  glass  stopper,  will  serve  the  same  end. 
If  a  mineral  analysis  should  be  required,  it  is  necessary  to  have 
quite  2  gallons  of  the  water.  It  is  well  to  avoid  the  employment 
of  stoneware  bottles. 

The  bottle  must  be  thoroughly  cleansed  by  first  well  rinsing 
with  a  little  dilute  hydrochloric  acid,  and  then  by  washing  in 
good  water  until  the  washings  are  no  longer  acid. 

In  collecting  a  sample  the  bottle  is  first  quite  filled  with  the 
water,  and  then  emptied;  it  is  again  almost  completely  filled  up 
(in  a  manner  which  will  not  favour  the  aeration  of  the  water), 
and  the  glass  stopper,  having  been  found  to  fit  accurately  and 
tightly,  is  well  rinsed  in  the  water  before  it  is  inserted,  when  it  is 


THE  COLLECTION  OF  SAMPLES  21 

tied  down  firmly  on  to  the  neck  of  the  bottle  and  the  knots  are 
protected  with  seahng-wax.  Care  is  taken  to  keep  the  sample 
cool  and  unexposed  to  light  until  the  analysis  is  commenced;  and 
under  no  circumstances  should  some  of  the  estimations  be  un- 
necessarily delayed,  as  important  chemical  changes  may  occur — 
i.e.,  organic  matter  may  suffer  a  very  slight  reduction,  free 
ammonia  may  increase  or  decrease  in  amount,  nitrates  may  be 
reduced  or  even  increased,  calcium  or  magnesium  carbonates 
and  iron,  which  were  held  in  solution  by  carbonic  acid,  may, 
owing  to  the  escape  of  the  carbonic  acid,  be  partially  deposited. 
Therefore  the  figures  of  the  two  ammonias,  the  oxidizable  organic 
matter  and  of  the  oxidized  nitrogen,  together  with  the  physical 
characters,  should  always  be  ascertained  as  soon  as  possible  (and 
certainly  within  forty-eight  hours)  after  the  sample  has  been 
collected. 

Information  required  as  to  Samples. 

It  is  often  difficult  to  form  a  correct  opinion  upon  the  purity 
of  a  sample  without  the  knowledge  of  some  of  the  circumstances 
of  its  source;  and  if  the  water  is  held  to  run  risk  of  harmful 
pollution  this  should  suffice  for  its  condemnation,  although  the 
chemical  analysis  at  the  time  may  prove  satisfactory;  natural 
agencies  may  suffice  to  purify  water  for  a  time,  but  there  is  always 
a  possibility  of  their  purifying  powers  being  exhausted  at  any 
moment,  and  the  danger  of  drinking  such  water  is  a  constant  one. 

Thus,  information  as  regards  the  risks  of  pollution  may  be  of 
great  value  as  indicating  possibilities  of  danger,  when  such  danger 
may  not  be  manifest  at  the  time  by  analysis;  it  is  also  of  value 
to  ask,  in  every  instance,  the  motive  for  requiring  an  analysis. 

Information  bearing  upon  the  constitution  of  the  strata 
through  or  over  which  the  water  has  passed  is  most  valuable, 
since  the  soluble  mineral  constituents  of  certain  strata  are  similar 
to  those  which  may  result  from  previous  organic  pollution. 
Anyone  is  able  to  furnish  information  as  to  whether  the  surface 
consists  of  such  familiar  substances  as  clay,  gravel,  sand,  chalk, 
or  vegetable  mould,  and  whether  the  subsoil,  exposed  as  it  is  by 
railway  or  road  cuttings,  is  of  chalk,  sandstone,  etc. 

It  is  very  desirable  that  labels  should  be  given  to  those  col- 
lecting samples,  and  that  these  should  be  affixed  to  the  bottle. 
The  subjoined  label,  when  filled  in,  would  convey  all  necessary 
information  to  the  analyst : 


22  LABORATORY   WORK 


Sample  of  Water  for  Analysis. 

Name  and  address  of  sender 

Place,  date,  and  hour  of  collection 

Source  of  sample  and  method  of  collection 

If  from  well,  give  approximate  depth 

and  geological  characters  of  the  soil  and  subsoil  of  the  district 

If  from  shallow  well,  give  the  rainfall  during  the  previous  week,  in 

such  terms  as  "  nil,"  "  small,"  or  "  great  "  in  amount 

Nature  and  distance  of    any  evident  or   possible  source  of  pollution 


Reason  for  tlcsiring  an  analj'sis. 


The  following  is  the  usual  form  of  report  upon  the  chemical 
examination  of  a  sample  of  water: 


Report  on  the  Analysis  of  a  Sample  of  Water  received  on. 
from and  labelled  .  .  . 


Number  of  sample   .  . 

Date  of  examination  .  .  .  .  .  .  ■  .  . 

Physical  characters 

Reaction    .  . 

Saline  and  free  ammonia 

Organic  (or  "  albuminoid  ")  ammonia.  . 

Oxygen  absorbed  from  permanganate  in  two  hours  at  27°  C. 

Chlorine 

Nitrogen  as  nitrates 

Total  solid  matter    .  . 

(a)  Volatile 
(fe)   Fixed 

Appearance  on  ignition 
Total  hardness 

{a)  Temporary.. 

(b)  Permanent.. 
Poisonous  metals 
Nitrites 
Phosphates 
Sulphates 

Microscopical  examination  of  the  sediment 


Opinion 


(Signed) 
Date 


SAMPLE    OF   WATER    FOR   ANALYSIS 


23 


Where  a  series  of  analyses  are  to  be  brouf^ht  into  comparison, 
the  following  form  of  report  is  to  be  preferred : 

Results  of  Analysis  expressed  in  Parts  i^kr  100,000. 


If 

0  I) 

Bi 
0 

c  2 

Organic  or 
Albuminoid 
Ammonia. 

Oxygen  absorbed 

in  Two  Hours 

at  27°  C. 

.S 

'u 

_o 
0 

Nitrogen  as 

Nitrates  and 

Nitrites. 

Hardness. 

Solids. 

B 

V 

>> 

2 
0 

a, 
6 

4) 

H 

c 

> 

T3 

rt 
0 
H 

The  result  of  every  analysis  should  be  carefully  entered  in  a 
book  kept  for  the  purpose,  for  such  a  record  becomes  most 
valuable  for  reference  purposes  and  for  making  comparisons 
with  future  samples  of  water  from  the  same  locality. 

The  results  of  the  estimations  made  in  water  analysis  are  still 
variously  returned  in  terms  of  grains  per  gallon  and  parts  per 
100,000. 

It  seems  desirable  that  uniformity  of  expression  should  be 
established.  Parts  per  100,000  is  the  most  common  return  made 
in  this  country,  and  it  is,  moreover,  in  general  use  in  France, 
Germany,  etc. 

It  is  easy  to  convert  grains  per  gallon  to  parts  per  100,000,  or 
vice  versa. 

Supposing  a  report  reads  "  chlorine  2-8  grains  per  gallon," 
how  many  parts  per  100,000  will  this  represent  ? 

There  are  70,000  grains  in  a  gallon.  Therefore  there  are 
2-8  grains  in  70,000  grains,  or  2-8  parts  per  70,000  parts,  or 
4  parts  per  100,000. 

It  is  only  necessary,  therefore,  to  multiply  results  returned 
in  "  grains  per  gallon,"  by  ten,  and  to  divide  by  seven,  in  order 
to  convert  them  into  "  parts  per  100,000,"  since  grains  per  gallon 
are  parts  per  70,000;  and  so,  to  convert  "parts  per  100,000"  to 
"  grains  per  gallon,"  the  returns  must  be  multiplied  by  seven 
and  divided  by  ten. 

Where  the  results  of  a  quantitative  test  are  returned  in  terms 
of  "  grains  per  gallon,"  it  is  convenient  to  work  with  70  c.c. 
of  the  sample.  The  reason  for  this  is  that  70  c.c.  represent  "a 
miniature  gallon,"  so  called,    and  the  results   can   at  once  be 


24  LABORATORY   WORK 

expressed  in  terms  of  an  imperial  gallon.  The  relation  between 
the  so-called  "  miniature  gallon  "  and  the  imperial  gallon  depends 
upon  the  following  facts: 

One  c.c.  of  water  is  taken  to  weigh  i  gramme.  Therefore 
70  c.c.  ("  the  miniature  gallon")  of  water  weigh  70  grammes, 
or  70,000  milligrammes. 

Therefore,  since  there  are  70,000  component  parts  in  each  case, 
the  milhgrammes  in  "  the  miniature  gallon  "  are  equivalent  to 
the  grains  in  the  imperial  measure. 

The  various  tests  emploj^ed  in  the  chemical  and  ph^^sical  ex- 
amination of  water  for  public  health  purposes  have  now  to  be 
considered.  But  it  must  be  fully  reahzed  that  organic  pollution 
will  give  evidence  of  its  presence  in  many  of  the  steps  which 
form  a  complete  analysis,  and  that  it  is  tliis  collective  evidence 
which  determines  the  opinion  to  be  formed,  and  not  the  evidence 
which  any  one  special  test  may  appear  to  offer. 


CHAPTER  II 

THE  PHYSICAL  CHARACTERS  OF  WATER 

Whereas  polluted  shallow-well  waters  are  notoriously  often 
clear,  sparkling,  and  pleasant  to  the  palate,  these  characters  are 
precisely  those  of  our  purest  and  best  waters.  For  this  reason, 
and  from  what  follows,  it  will  be  seen  that  the  evidence  of  purity 
furnished  by  the  senses  may  be  very  misleading.  Such  physical 
tests,  therefore,  are  not  worthy  of  lengthy  consideration. 

The  Physical  Characters. 

The  sample  is  first  well  shaken,  and  then  a  thin,  colourless 
glass  tube,  24  inches  long,  is  filled  with  the  water,  and  from  the 
appearance  of  this,  in  the  "  2-foot  tube,"  as  it  is  called,  the 
physical  characters  of  clearness  or  turbidity,  colour  and  the 
degree  of  aeration,  are  noted. 

1,  Clearness. — Though  the  best  waters  are  always  bright  and 
clear,  these  qualities  cannot  be  considered  as  evidence  of  purity, 
for  a  polluted  well  water  may  also  possess  them;  and,  on  the 
other  hand,  any  slight  haziness  or  turbidity — which  is,  of  course, 
furnished  by  minute  particles  of  suspended  matter — ^may  by 
chemical  and  microscopical  examination  be  proved  either  in- 
nocuous or  harmful.  Opacity  may  be  caused  by  clay,  iron,  chalk, 
lead,  or  vegetable  matter  in  suspension. 

It  is  difficult  to  satisfactorily  estimate  the  amount  of  turbidity. 
Generally  the  transparency  of  water  is  measured  by  ascertaining 
through  what  depth  of  liquid  a  black-and-white  figure  can  be 
seen  with  a  given  intensity  of  light.  The  degree  of  any  such 
turbidity  may  be  expressed  as  "  very  slightly  turbid,"  "  slightly 
turbid,"  and  "  turbid." 

2.  Colour. — To  detect  this  the  tube  is  fixed  vertically  so  as  to 
stand  upon  a  white  porcelain  slab,  and  the  observer  looks  down 
through  the  depth  of  the  column  of  water  on  to  the  slab,  which 

25 


26  LABORATORY   WORK 

then  forms  a  background.  It  is  only  in  this  matter  that  the 
faintest  degrees  of  coloration  are  best  appreciated,  if  even  they 
be  detected  at  all;  and  when  thus  examined  it  is  rare  that  the 
water  is  not  seen  to  possess  a  colour,  however  faint.  In  a  good 
water  it  is  generally  of  an  extremely  faint  greyish-blue  or  greenish 
tint.  Filtration  of  the  water  would  show  whether  any  colour  is 
due  to  suspended  or  dissolved  matter. 

The  colour,  which  is  most  marked  in  water  from  reservoirs, 
lakes,  and  rivers,  tends  to  a  greenish  hue  in  the  spring  and  a 
brown  in  the  autumn  and  winter. 

The  various  hues  of  j^ellow  and  brown  will  denote  either  the 
presence  of  animal  or  vegetable  pollution  {i.e.,  sewage  or  peat), 
or  mineral  contamination  such  as  iron  or  clay;  but  if  such  colour 
is  due  to  iron  or  clay  a  sediment  will  form.  Clear  waters  from  a 
depth  which  turn  to  a  brownish-yellow  colour  on  standing  contain 
iron,  the  soluble  ferrous  salts  becoming  oxidized  to  insoluble 
ferric  salts. 

The  amount  of  sewage  pollution  must  be 'enormous  to  furnish 
any  colour,  and  a  brownish  tint  in  waters  used  for  drinking 
purposes  is  generally  due  to  peat  or  iron. 

A  brown  or  red  colour  associated  with  turbidity  and  odour 
is  often  due  to  the  growth  of  Crenothrix  polyspora,  a  microscopic 
vegetable  growth  consisting  of  massed  zooglceae  and  slender 
cobweb-like  filaments.  The  organisms  form  a  great  number 
and  diversity  of  spores,  and  hence  its  specific  name  of  polyspora. 
The  growth  is  rich  in  iron. 

A  marked  green  denotes  the  presence  of  vegetable  matter 
containing  chlorophyll,  which  will  generally  be  found  to  consist 
of  the  harmless  algae. 

A  blue-green  tint  in  water,  associated  with  a  iloating  bright 
green  scum,  has  been  found  to  be  due  to  a  species  of  Anabcena 
in  association  with  a  monad  (Garrett). 

Red  rain — in  which  the  colour  was  produced  by  dust  (prob- 
ably of  cosmic  origin) — fell  in  some  parts  of  Europe  in  igoi. 
Rain  water  has  also  been  coloured  by  volcanic  ash  and  by  desert 
sand;  and  "  bloody  "  snow,  produced  by  growths  of  Palmella 
sanguinea,  has  been  described. 

A  red  colour  has  been  found  to  be  due  to  an  alga  named 
Oscillatoria  rubescens. 

Colour  alone  affords  no  justification  for  condemning  a  water 
as  unfit  for  drinking  purposes  until  the  nature  of  the  material 


THE   PHYSICAL   CHARACTERS   OF   WATER  27 

furnishing  it  is  known;  peat,  for  example,   present  to  quite  a 
harmless  extent,  will  often  colour  a  water  markedly. 

The  importance  of  the  test  does  not  seem  to  warrant  any 
attempt  at  definite  measurement  when  isolated  examples  are 
examined;  but  this  is  of  service  as  a  rough  indication  of  the 
working  efficiency  of  filtration  processes  in  the  case  of  some 
waters.  If  such  a  test  is  desired  it  is  best  performed  by  the 
method  of  Crookes,  Odling,  and  Tidy.  In  this  method  an  empty 
tube,  exactly  similar  in  every  respect  to  one  containing  the  water 
to  be  compared,  is  employed;  this  has  two  hollow  glass  wedges 
behind  it,  the  one  filled  with  |  per  cent,  sulphate  of  copper 
solution,  and  the  other  with  a  mixture  of  ferric  chloride 
(0-7  gramme  per  Htre)  and  cobalt  chloride  (0-3  gramme  per  litre), 
with  a  very  slight  excess  of  hydrochloric  acid.  These  wedges  are 
made  to  slide  across  one  another  in  front  of  a  circular  aperture  in 
a  metal  sheet;  and  thus  any  desired  combination  of  brown  and 
blue  can  be  obtained.  They  are  pushed  over  the  empty  tube 
until  the  colour,  on  looking  down  it,  appears  to  be  identical  with 
that  of  the  water-tube.  Each  prism  is  graduated  from  i  to  50, 
the  figures  indicating  millimetres  in  depth  of  the  solution  at  that 
particular  part  of  the  prism,  and  the  degree  of  colour  is  expressed 
as  equivalent  to  so  many  millimetres  of  blue  and  so  many  of 
brown  solution. 

3.  Taste. — The  pleasant  taste  of  good  water  is  furnished  by 
the  gases  dissolved  in  it;  but  since  water  must  contain  large 
quantities  of  any  ingredient  for  its  presence  to  be  detected  by 
the  sense  of  taste,  as  an  indication  of  dangerous  contamination 
the  test  is  useless.  One-quarter  grain  to  the  gallon  of  iron  will 
impart  a  faint  chalybeate  flavour,  and  this  amount  should  not 
be  exceeded  in  a  drinking-water.  Chloride  of  sodium  (common 
salt)  may  be  present  in  enormous  quantities  (80  to  90  parts  per 
100,000)  without  causing  a  brackish  taste;  and  waters  foully 
polluted  with  organic  matters  are  often  so  palatable  that  they 
have  frequently  been  preferred  by  the  public  to  much  purer 
waters. 

Certain  vegetable  growths  (Anahcena  and  Tahellaria)  may  be 
the  cause  of  unpleasant  tastes. 

It  is  not  advisable,  as  a  rule,  to  taste  samples  sent  for  analj^sis. 

4.  Odour. — This  is  best  detected  by  nearly  filling  a  200  c.c. 
glass-stoppered  bottle  (itself  odourless),  almost  completely  im- 
mersing this  in  hot  water  at  about  60°  C.  for  a  few  minutes,  and 


28  LABORATORY   WORK 

then  noting  any  odoni^  immediately  on  removing  the  stopper. 
The  prehminary  addition  to  the  water  of  a  httle  strong  potassic 
hydrate  solution  helps  to  make  the  test  more  sensitive.  For 
most  practical  purposes,  however,  it  will  suffice  to  smell  the 
sample  after  it  has  been  thoroughly  shaken;  and  it  is  only 
necessary  to  resort  to  the  plan  of  heating  the  water  when  a  sus- 
picion remains  after  this  procedure,  or  when  there  is  strong  reason 
for  considering  that  odoriferous  gases  may  be  present  in  small 
quantities  inappreciable  except  when  disengaged  by  heat. 

The  test  of  odour  is  unreliable,  and  none  may  be  evident  in 
waters  which  are  grossly  polluted  by  sewage;  it  must  be  borne 
in  mind,  moreover,  that  many  of  the  noxious  materials  which  may 
gain  access  to  a  water  have  little,  if  any,  odour  originally. 
.  The  variety  of  odours  which  may  be  given  off  from  a  water 
defies  description;  many  of  them,  though  quite  peculiar  and 
distinct,  it  is  impossible  to  describe,  and  any  comparisons  made 
with  other  odours  are  not  always  appreciated;  but  under  any 
circumstances  the  analyst  should  attempt  to  describe  the  odour 
in  his  own  words. 

Many  odours  are  due  to  the  growth  of  minute  organisms,  more 
especially  algae.  Anahcena  and  Tahellaria  may  give  rise  to  un- 
pleasant odours,  also  Cryptomonas  and  other  protozoa.  To 
favour  a  large  growth  of  algae  the  water  must  be  stagnant  and 
quiescent  (as  in  ponds  and  reservoirs)  in  situations  sheltered  from 
the  wind. 

Such  terms  as  "  musty,"  "  horse-pond-like,"  "  pig-odour," 
"fishy"  "cucumber-like,"  "grassy,"  "earthy,"  etc.,  have  been 
employed  to  denote  the  odour  in  certain  pond  waters.  Some  of 
these  odours  are  related  to  essential  oils,  and  are  produced  by 
living  organisms;  others  result  from  the  decay  of  the  bodies  of 
these  organisms. 

A  distinctly  putrid  odour  is  characteristic  of  large  quantities 
of  decomposing  animal  or  vegetable  matter,  and  a  urinous  odour 
is  sometimes  perceptible  when  large  quantities  of  fresh  sewage 
have  gained  access  to  water.  The  rotten-egg  odour  of  sulphu- 
retted hydrogen  and  that  of  coal-gas  are  both  peculiar  and  dis- 
tinctive. The  presence  of  any  of  these  odours  would  condemn 
the  water,  except  in  the  case  of  waters  from  a  depth  naturally 
charged  with  sulphuretted  hydrogen  and  free  from  animal 
pollution  (as  at  Harrogate,  etc.). 

The  fishy  odour  is  generally  due  to  infusorians  {Uroglena  and 


THE    PHYSICAL   CHARACTERS    OF   WATER  29 

other  protozoa,  Volvox,  etc.),  but  it  may  arise  from  decomposing 
algae.  Apparently  it  may  also  be  due  to  small  water-snails; 
and  the  introduction  of  trout  to  reservoirs  thus  affected  has,  by 
keeping  down  their  numbers,  led  to  a  cure.  Crenothrix,  a  fungoid 
plant  which  grows  in  the  presence  of  protosalts  of  iron  and 
decomposing  organic  matter,  has  often  given  rise  (hke  Beggiatoa) 
to  disagreeable  odour  (SH2)  and  taste  in  public  water-supplies, 
especially  in  the  late  summer  and  autumn.  Small  water-eels 
in  water-pipes  have,  by  their  decomposition,  occasioned  evil 
odours  in  waters. 

Sulphuretted  hydrogen  may  mask  other  odours;  the  addition 
of  a  little  copper  sulphate  solution  will  prevent  this  and  produce 
a  brownish  discoloration  (due  to  CuS). 

As  a  rule  the  most  frequent  and  objectionable  odours  are 
developed  in  surface  waters. 

5.  Aeration. — Evidence  of  this  is  afforded  by  the  amount  of 
lustre  the  water  possesses.  Coarser  degrees  of  aeration  are  noted 
by  minute  air  bubbles  collecting  at  the  sides  and  bottom  of  the 
2-foot  tube,  and  rising  up  occasionally  through  the  water  to  the 
surface.  Waters  from  the  chalk  and  limestone  formations  con- 
tain much  carbonic  acid,  and  little  of  any  other  gas;  and  where 
the  water  from  these  strata  has  been  subjected  to  conditions  of 
high  pressure  and  low  temperature,  carbonic  acid  may  even  be 
in  such  quantities  as  to  give  a  white  turbidity  to  the  water  when 
this  is  first  exposed  to  the  air. 

The  degree  of  aeration  is  of  no  value  by  itself  in  the  estimation 
of  the  purity  or  impurity  of  a  water,  though  a  good  water,  to  be 
palatable,  must  be  well  aerated.  Many  deep-well  and  spring 
waters,  of  great  purity,  are  poorly  aerated,  and  many  foul  waters 
are  particularly  bright  and  sparkling  (chiefly  from  carbonic  acid 
derived  from  organic  decomposition). 

6.  Reaction. — This  is  important,  not  so  much  as  affecting  an 
opinion  upon  the  wholesomeness  of  the  water  as  from  the  circum- 
stance that  it  determines  the  effect  which  the  water  may  have 
upon  lead,  iron,  and  zinc  surfaces,  and  because  in  some  steps  of 
the  analysis  it  becomes  necessary  to  neutralize  any  acidity  in  the 
sample.  Most  waters  markedly  polluted  with  animal  matter  are 
decidedly  alkaline  from  the  carbonate  of  ammonia  furnished  by 
urine  decomposition.  The  maj  ority  of  pure  waters  in  this  country 
are  faintly  alkahne,  the  alkahnity  being  most  generally  given 
by  calcium  carbonate,  and  less  often  by  sodium  carbonate,  etc. 


30  LABORATORY   WORK 

Some  waters  will  be  found  to  be  neutral  in  reaction,  and  acid 
waters  are  bj-  no  means  uncommon  in  this  country;  the  latter 
most  frequentl}'  obtain  their  acidit}^  from  the  peaty  acids  (the 
humic,  ulmic,  and  geic)  taken  up  from  the  decaying  vegetable 
matter  encountered  in  their  surface  flow,  and  such  acidity  is  a 
characteristic  feature  of  so-called  "  peaty  "  waters.  It  is  most 
marked  after  long  periods  of  dr}^  weather. 

The  reaction  may  be  obtained  by  partially  immersing  in  the 
water,  pieces  of  delicate  blue  and  red  litmus-papers,  and  noting 
the  change  after  a  few  minutes. 

If  the  water  gives  an  acid  reaction,  it  should  be  boiled,  allowed 
to  cool,  and  tested  again.  If  the  acidity  has  been  lost,  it  was 
due  to  free  carbonic  acid.  Any  free  acid  in  water  is  most  gener- 
ally carbonic  acid  or  organic  acids,  but  it  may  also  be  sulphuric 
acid.  The  sulphuric  acid  may  gain  access  to  water  from  the 
oxidation  of  iron  pyrites  (sulphides)  in  the  soil,  or,  like  other 
acids,  from  the  waste  of  factories;  or  in  small  amount  from  the 
sulphur  in  the  coal  burnt  when  rain-water  washes  the  atmosphere 
over  a  town.  Alkahnity  that  disappears  on  boihng  is  due  to  free 
ammonia. 

It  is  not  generally  necessary  for  hygienic  purposes  to  test  the 
degree  of  alkalinity  or  acidity  of  the  water,  but  it  is  sometimes 
useful  to  make  such  an  estimation,  and  the  method  is  set  forth 
in  Chapter  XVI. 

7.  The  Sediment. — ^The  presence  of  this,  together  with  its 
macroscopic  appearance,  should  be  noted  at  this  stage,  but  any 
opinion  of  its  nature  must  be  reserved  until  a  microscopic  and 
chemical  examination  have  been  made  {vide  Chapter  VIII.). 
Certain  waters  deposit  calcium  carbonate  or  iron  when  allowed 
to  stand  exposed  to  the  air;  this  is  due  to  the  escape  of  the 
carbonic  acid  which  held  these  substances  in  solution. 

8.  Temperature. — Sometimes  spring  water  from  a  great  depth 
is  warm  or  even  hot.  This  is  due  to  the  fact  that,  below  the 
level  at  which  variations  due  to  atmospheric  alternations  of 
temperature  cease  to  be  recognizable,  the  temperature  of  the 
earth  increases  with  the  depth  when  the  measurement  commences 
a  few  feet  from  the  surface,  the  water  temperature  rising  about 
1°  F.  for  every  50  to  60  feet  of  depth,  on  an  average.  The 
temperature  of  water  may  furnish  a  useful  indication  of  its 
source  as  well  as  the  depth  from  which  it  issues. 


CHAPTER  III 

CHLORINE 

Chlorine  exists  in  most  waters  as  chloride  of  sodium,  potassium 
or  calcium.  Rarely  free  chlorine  has  been  found  in  waters 
polluted  by  industrial  waste  products. 

This  combined  chlorine  is  present  in  all  waters  to  a  small 
extent,  even  in  rain  water.  In  the  rain  water  of  country  districts 
the  chlorine  varies  from  o-2  to  0-5  part  per  100,000. 

The  presence  of  combined  chlorine  in  water  in  excess  of  this 
amount  is  due  to  one  of  the  following  causes : 

(a)  The  water  has  previously  percolated  strata  which  yield 

chlorides,  such  as  greensand,  sandstone,  the  London 
clay,  chalk,  etc.  In  the  districts  of  salt  deposits  and 
in  certain  districts  near  the  coast  the  well  water  may 
contain  very  large  quantities  of  chlorides. 

(b)  Pollution   by   animal   organic   matter,    and   chiefly   urine 

(which  contains  nearly  i,  per  cent,  of  chlorides). 

(c)  Admixture  with  sea  water,  as  in  tidal  rivers,  and  occasion- 

ally deep  wells  by  the  sea-coast. 

(d)  Open  reservoirs  and  other  expanses  of  fresh  water  stored 

near  the  coast  take  up  chlorides  in  appreciable  amount 
from  the  atmosphere.  It  may  also  happen  that  large 
collections  of  rain  water  show  a  chlorine  figure  con- 
siderably above  that  in  the  rainfall  of  the  district,  even 
when  they  are  not  situated  near  the  coast.  This  cir- 
cumstance is  accounted  for  by  the  concentration  which 
the  water  is  always  undergoing  on  account  of  the 
evaporation  from  its  surface. 
{e)  Effluents  from  alkali  and  other  industrial  works. 

Thus  where  it  is  possible  to  exclude  sources  {a),  (c),  and  (e),  the 
presence  of  chlorine  in  excess  of  i  part  per  100,000  may  be  taken 

31 


32  LABORATORY   WORK 

to  indicate  organic  contamination  (past  or  present),  and  that  of 
an  animal  nature,  since  vegetable  pollution  fer  se  furnishes  no 
such  excess;  hence  clilorine  often  serves  to  indicate  whether  a 
vitiated  water  is  polluted  by  animal  or  by  vegetable  matter. 

It  remains  now  to  be  seen,  apart  from  other  information  which 
is  available,  what  chemical  means  there  are  of  excluding  causes 
{a),  (c),  and  (e)  as  furnishing  chlorine  in  excess  of  the  amount  in 
pure  rain  and  surface  waters.  When  the  excess  is  derived  solely 
from  the  strata,  there  \\dll  be  no  evidence  of  organic  pollution 
furnished  by  the  other  steps  of  the  analysis.  If,  on  the  other 
hand,  the  excess  be  due  to  animal  pollution,  there  will  be 
further  evidence  of  this  contamination  in  all  those  steps  of  the 
analysis  which  serve  to  indicate  such  pollution.  The  amount 
of  chlorine  originally  taken  up  from  animal  pollution  is  not 
reduced  by  subsequent  filtration  of  the  water  through  subsoil  or 
strata. 

Finally,  if  the  excess  of  chlorine  be  due  to  admixture  with  sea 
water,  there  will  also  be  present  large  quantities  of  magnesium 
salts,  and  this  fact  will  at  once  indicate  its  source. 

Qualitative  Test  and  Quantitative  Estimation. 
Special  Apparatus  required : 

A  white  porcelain  dish, 

A  loo  c.c.  graduated  flask. 

A  burette  graduated  to  iVths  of  c.c.'s. 

A  glass  stirring-rod. 

Special  Chemical  Reagents  required : 

1.  a  cold  saturated  solution  of  the  yellow  chromate  of  potassium,  which 
must  be  free  from  chlorine ;  this  may  be  proved  by  acidulating  a  little  of 
the  solution  by  dilute  nitric  acid,  and  then  adding  a  drop  of  nitrate  of  silver 
solution;  in  the  absence  of  chlorine  the  solution  will  remain  perfectly 
clear. 

2.  A  standard  solution  of  silver  nitrate,  made  to  the  strength  that 
I  c.c.  is  capable  of  precipitating  i  milligramme  of  chlorine.  This  is  made 
by  dissolving  4-79  grammes  of  pure  recrystallized  silver  nitrate  in  distilled 
water,  and  then  making  up  to  a  litre.  The  solution  should  be  kept  in  a 
brown-coloured  bottle. 

The  reason  why  4-79  grammes  of  silver  nitrate  are  required  to  the  litre 
of  water  is  as  follows:  CI  (35-46)  combines  with  AgNOj  (i69-89).  There- 
fore I  part  of  chlorine  combines  with  (  =  )  4-79    parts    of    AgNO^. 

\  35'4"      / 
Thus  a  litre  of  distilled  water  containing  4*79  grammes  AgN03  will  pre- 
cipitate I  gramme  of  chlorine,  and  i  c.c.  will  precipitate  i  milligramme  of 
chlorine- 


GHLORlNit  33 

Qualitative  Test. 

The  presence  of  chlorine  (as  chlorides)  may  be  best  detected 
by  the  addition  of  a  few  drops  of  a  solution  of  silver  nitrate  and 
of  dilute  nitric  acid  to  the  water  in  a  test-tube,  when  a  white 
haze,  turbidity,  or  precipitate  of  chloride  of  silver  will  appear, 
according  to  the  amount  of  chlorine  present : 

AgN03  +  NaCl=AgCl  +  NaN03. 

Quantitative  Estimation. 

1.  Measure  out  lOO  c.c.  of  the  water  in  a  graduated  flask,  and 
pour  into  a  white  porcelain  dish. 

2.  Add  a  few  drops  of  the  solution  of  yellow  chromate  of 
potassium  until  a  distinct  yellow  colour  is  furnished  to  the  water. 
The  object  of  adding  this  reagent  is  to  make  it  serve  as  an 
"  indicator,"  which  shall  denote  at  once  the  stage  when  all 
the  chlorine  present  in  the  water  has  combined  with  the 
silver  employed  in  the  estimation. 

3.  The  burette  is  charged  with  the  standard  solution  of  nitrate 
of  silver,  and  this  is  added  drop  by  drop  to  the  water;  a  dull 
reddish  precipitate  of  the  red  silver  chromate  forms,  which  when 
stirred  up  in  the  water  by  means  of  a  glass  rod  at  once  dis- 
appears, owing  to  the  chlorine  in  the  water  displacing  the  chromic 
acid  and  itself  combining  with  the  silver  to  form  a  white  pre- 
cipitate of  the  chloride  of  silver.  As  the  addition  of  the  standard 
solution  is  continued,  the  water,  though  it  retains  the  yellow 
colour,  becomes  turbid,  owing  to  the  accumulation  of  this  pre- 
cipitate of  silver  chloride.  At  length  a  point  is  reached  at  which, 
there  being  no  longer  any  chlorine  which  is  not  already  combined 
with  the  silver,  the  chromic  acid  holds  undisputed  possession  of 
this  metal,  and  the  red  silver  chromate  remains  permanently 
present;  the  first  evidence  of  this  is  afforded  by  the  yellow  colour 
changing  into  a  permanent  orange  colour  (K2Cr04  +  3AgN03  = 
2KN03  +  Ag,Cr04). 

Without  the  "  indicator  "  there  would  be  no  means  of  knowing 
when  just  the  amount  of  silver  nitrate  necessary  to  precipitate 
all  the  chlorine  had  been  added;  for  it  would  be  impossible  to 
judge  of  the  exact  stage  when  the  maximum  amount  of  white 
precipitate  of  silver  chloride  had  been  created. 

3 


34  LABORATORY   WORK 

4.  The  first  evidence  of  any  red  colour  remaining  permanent 
is  the  clue  for  withholding  any  further  addition  of  the  silver 
nitrate;  or  the  amount  of  chlorine,  estimated  as  it  is  from  the 
amotint  of  the  solution  of  the  silver  salt  used,  will  be  overesti- 
mated. 

Example. — Five  c.c.  of  the  standard  solution  of  silver  nitrate 
were  required  to  combine  with  all  the  chlorine  in  100  c.c.  of 
water,  and  to  furnish  a  reddish  tint  to  the  water. 

But  I  c.c.  of  the  solution  =  i  milligramme  of  chlorine. 

.•.  5  c.c.  of  the  solution  =  5  milligrammes  of  chlorine. 

.•.  there  are  5  milligrammes  of  chlorine  in  100  c.c.  of 
water. 

But  100  c.c.  of  water  =  100  grammes  =  100,000  milligrammes. 

.-.  there  are  5  milligrammes  of  chlorine  in  100,000  milligrammes 
of  water;  or  5  parts  per  100,000. 

Conclusions  to  he  Drawn  from  the  Amount  Estimated. — It  must 
always  be  borne  in  mind  that  chlorine  can  only  be  attributed  to 
animal  organic  pollution  when  other  figures  of  the  analysis  point 
to  the  probability  of  such  an  origin.  Some  pure  chalk  and  red 
sandstone  waters  furnish  chlorine  up  to  5  parts  per  100,000.  In 
the  coal-measures  and  certain  chalk  and  sandstone  formations, 
low -lying  and  near  the  coast,  the  water  may  contain  up  to  50  parts 
of  chlorine  per  100,000;  or,  on  the  other  hand,  very  little  indeed. 
Pure  deep-well  waters  from  greensand  deposits  may  y'\t\6.  as 
much  as  15  parts  per  100,000,  or  more.  Upland  surface  waters 
free  from  animal  pollution  rarely  furnish  more  than  i  part  per 
100,000. 

Thresh  is  of  opinion  that  as  much  as  100  parts  per  100,000 
of  salt  should  condemn  the  water  for  drinking  purposes.  This 
amount  imparts  a  distinct  saline  taste. 

Notes. — Some  workers  deduct  o-i  c.c.  for  the  excess  of  silver 
solution  required  to  indicate  the  change  of  colour. 

It  is  highly  important  that  neither  the  water  nor  the  standard 
solution  of  silver  nitrate  should  be  acid,  or  the  results  will 
be  incorrect,  since  red  silver  chromate  is  soluble  in  an  acid 
medium.  In  these  cases  the  smallest  quantity  of  precipitated 
calcium  carbonate  that  will  suffice  should  be  added  to  effect 
neutrality. 

In  estimating  very  small  quantities  of  chlorine  it  is  advisable 
to  first  concentrate  the  water  before  titrating,  as  the  results  are 
otherwise  very  slightly  in  excess. 


CHLORINE  35 

Those  who  have  not  a  keen  appreciation  of  colour  change 
may  prepare  a  second  lOO  c.c.  of  water,  to  which  a  precisely 
similar  amount  of  the  chromate  has  been  added;  if  this  is 
placed  alongside  the  water  under  examination,  it  serves  as  a 
comparison  whereby  to  judge  the  commencement  of  the  colour 
change. 

Coloured  waters  may  be  bleached  in  acid  solution  by  means  of 
potassium  permanganate;  the  water  is  then  neutralized  and  fil- 
tered before  the  chlorine  is  estimated. 

The  chlorine  is  sometimes  expressed  in  terms  of  the  common 
salt  it  is  equivalent  to.  This  is  readily  calculated  by  a  com- 
parison between  the  atomic  weight  of  chlorine  and  the  molecular 
weight  of  NaCl  (common  salt). 

The  atomic  weight  of  chlorine  is  35-46,  and  that  of  sodium  is 
23-00;  .-.  the  molecular  weight  of  NaCl=  (35-46 +  23-00)=  58-46. 

•••Cl=J|^ofNaCl. 
58-46 

Now,  the  chlorine  in  the  example  taken  amounted  to  5  parts 

per  100,000;  then  5"^^^  NaCl, 

orNaC1^5^5^8..4. 

.-.  there  would  be  present  8-24  parts  of  NaCl  per  100,000  if  all 
the  chlorine  present  were  furnished  by  sodium  chloride.     Thus 

the  weight  of  chlorine  x  (        ^  =  j  i  -65  =  the  weight  of  sodium 

chloride. 

In  the  State  of  Massachusetts  it  is  found  that  the  chlorine 
in  the  surface  waters  and  streams  decreases  in  amount  with  the 
distance  from  the  sea-board.  The  normal  chlorine  in  waters  free 
from  all  risks  of  pollution  has  been  ascertained  for  each  district, 
and  these  amounts  are  entered  on  a  map  of  the  State.  Lines 
have  been  drawn  connecting  the  districts  the  waters  of  which 
contain  similar  quantities  of  chlorine,  and  these  are  termed 
"  isochlors."  If  the  chlorine  in  any  water  is  found  to  exceed  the 
normal  of  the  district  from  which  it  has  been  obtained,  the  pre- 
sumption is  that  the  water  is  polluted  with  sewage.  But  a 
chlorine  test  is  by  no  means  delicate  enough  to  indicate  the 
lesser  degrees  of  dangerous  animal  contamination. 


3^  LABORATORY   WORK 

The  percentage  admixture  of  sea  water  with  fresh  water  may 

A-C 

be  calculated  from  the  formula  x^  r  —  T\'  '^^^^^ 

;v=the  number  of  volumes  of  fresh  water  to  i  volume  of 

sea  water; 
A=the  chlorine  in  sea  water  (wliicli  may  be  taken  as  1,850 

parts  per  100,000); 
B=  the  chlorine  in  the  local  fresh  water; 
C  =  the  chlorine  in  the  mixture  of  fresh  water  and  sea  water. 


CHAPTER  IV 

HARDNESS 

The  "  hardness  "  of  water  is  of  economic  rather  than  of  hygienic 
importance,  and  the  main  object  of  the  estimation  is  to  decide 
whether  the  amount  of  hardness  is  such  as  to  render  the  water 
unsuitable  for  washing,  cooking,  and  trade  purposes.  A  hard 
water  entails  in  its  use  a  great  waste  of  soap,  for  considerable 
difficulty  is  experienced  in  procuring  a  lather  (i  grain  of  calcium 
carbonate  will  use  up  8  grains  of  soap  before  a  lather  forms) ;  it 
does  not  extract  the  same  amount  of  strength  from  coffee,  tea- 
leaves,  and  substances  used  for  making  soups,  stews,  and  gravies, 
as  softer  water;  and  meat  and  vegetables  boiled  in  it  lose  much 
of  their  flavour  and  colour,  become  slightly  hardened  and  less 
digestible.  On  the  other  hand,  moderately  hard  waters  are 
always  more  palatable  than  very  soft  ones. 

It  must  not  be  thought,  however,  that  "  hardness  "  in  a  water 
is  a  factor  which  can  be  altogether  disregarded  from  a  health 
standpoint,  for  gastro-intestinal  derangement,  of  a  degree  vary- 
ing with  the  constitution  of  the  salts  which  form  the  "  hardness," 
may  arise  among  those  who  are  constitutionally  susceptible,  and 
unaccustomed  to  a  very  hard  water.  The  "  permanent  hard- 
ness "  is  generally  mainly  due  to  sulphates  of  the  alkaline  earths, 
and  these  have  a  marked  aperient  action,  when  they  exist  in 
large  amounts.  Such  waters  are  obtainable  at  Epsom,  Leam- 
ington, Scarborough,  and  Cheltenham. 

Finally,  hard  waters  form  a  deposit  on  boilers  and  in  pipes; 
and  this  is  sometimes  the  cause  of  explosions  and  demands 
occasional  removal.  It  is  calculated  that  ^  inch  of  the  incrusta- 
tion— which  is  a  bad  conductor  of  heat — requires  the  use  of 
45  per  cent,  of  extra  coal. 

For  trade  purposes  generally — apart  from  the  waste-  of  fuel, 
damage  to  boilers  and  danger  occasioned  by  the  "  crust  "  from 

37 


38  LABORATORY  WORK 

hard  waters — it  is  of  great  importance  to  the  process  itself  that 
the  water  should  be  moderate^  soft. 

The  factors  which  commonly  cause  the  total  "  hardness  "  in 
water  are  the  following: 

Calcium  and  magnesium  salts;  iron,  silica,  and  alumina;  free 
carbonic  acid,  or  free  mineral  or  vegetable  acids. 

The  "  total  hardness  "  in  most  of  the  drinking-waters  of  this 
country  is  largely  furnished  by  calcium  and  magnesium  salts,  and 
free  carbonic  acid;  and  more  especially  to  calcium  salts. 

Of  the  calcium  and  magnesium  salts,  the  carbonates  very 
greatly  predominate  as  the  cause  of  "  hardness."  These  car- 
bonates of  calcium  and  magnesium,  almost  insoluble  in  pure 
water,  are  held  in  solution  b}^  carbonic  acid,  in  the  form  of 
bicarbonates. 

If  the  water  be  well  boiled,  some  of  the  salts  forming  the 
total  hardness  usually  become  precipitated,  and  being  no  longer 
in  solution,  they  cease  to  add  to  the  "total  hardness";  the 
amount  of  hardness  thus  removed  is  termed  "  temporary,"  and 
that  remaining  "  permanent."  By  boiling,  the  carbonic  acid 
which  held  the  carbonates  of  calcium  and  magnesium  in  solution 
is  driven  off,  so  that  these  salts  precipitate.  Any  other  con- 
stituent which  may  have  been  held  in  solution  by  the  carbonic 
acid  present,  such  as  iron,  would  also  be  precipitated.  Phosphate 
of  lime,  sihca,  and  the  sulphate  of  lime  (if  present  in  large  quan- 
tity) maj'  also  in  part  be  precipitated. 

The  "  permanent  hardness"  results  from  what  still  remains 
in  solution — i.e.,  calcium  and  magnesium  sulphates,  phosphates, 
chlorides  and  nitrates,  an}'  iron  which  was  not  held  in  solution  by 
CO2,  silica,  alumina,  etc.  A  little  of  the  magnesium  carbonate 
thrown  down  by  the  boiling  will,  moreover,  become  redissolved 
by  the  time  the  water  cools,  and  thus  may  add  to  the  "  per- 
manent "  hardness. 

Although  the  amount  of  mineral  solids  which  the  water  con- 
tains generally  forms  an  index  to  the  extent  of  "  hardness," 
3"et  this  is  by  no  means  always  the  case;  and  some  sahne  waters 
yielding  considerable  quantities  of  mineral  matter  are  "  soft," 
a  large  quantity  of  sodium  salts  determining  the  softness. 

The  salts  causing  temporary  hardness  tend  to  furnish  a  loose 
deposit  in  boilers;  those  causing  permanent  hardness,  a  hard 
deposit. 


HARDNESS  39 

Quantitative  Estimation, 
Special  Apparatus  required : 

A  small  glass-stoppered  bottle  of  about  150  c.c.  capacity. 

A  burette  with  c.c.'s  graduated  to  J  c.c. 

A  glass  beaker. 

Filtering  apparatus. 

Iron  tripod,  wire  gauze,  and  triangle  lined  with  pipeclay. 

Special  Chemical  Reagents : 

A  standard  solution  ol  potassic  soap  or  of  good  undried  Castile  soap, 
made  to  such  a  strength  that  i  c.c.  will  exactly  precipitate  either  i  milli- 
gramme of  calcium  carbonate  or  those  other  soap-destroying  agents  in 
the  water  to  an  extent  which  is  equivalent  to  i  milligramme  of  calcium 
carbonate. 

Fourteen  grammes  of  Castile  soap  are  dissolved  up  in  a  litre  of  a  mixture 
of  equal  volumes  of  methylated  rectified  spirit  and  warm  distilled  water; 
it  is  then  filtered  and  standardized  (and,  being  unstable,  should  be  re- 
standardized  every  few  days)  by  means  of  a  standard  solution  of  calcium 
chloride. 

The  calcium  chloride  solution  is  made  by  dissolving  0-2  gramme  of  pure 
crystaUized  calcite  (CaCOg)  in  dilute  hydrochloric  acid.  When  this  is 
completely  dissolved,  evaporate  to  dryness  on  a  water-bath;  then  add  a 
little  distilled  water  and  again  evaporate  to  dryness,  and  repeat  this  treat- 
ment several  times  to  insure  that  all  the  acid  has  been  driven  off.  The 
calcium  chloride  is  then  dissolved  in  a  litre  of  distilled  water.  Such  a 
solution  will  then  contain  the  equivalent  to  0*2  milligramme  of  calcium 
carbonate  in  every  cubic  centimetre,  or  20  milligrammes  per  100  c.c. 

The  soap  solution  must  then  either  be  fortified  by  adding  a  little  strong 
solution  of  soap,  or  weakened  by  a  mixture  of  water  and  rectified  spirit 
(in  the  proportion  of  3  volumes  of  water  to  5  of  spirit),  until  the  soap 
solution  registers  hardness  equivalent  to  20  milligrammes  of  CaCOg  in 
100  c.c.  of  the  calcium  chloride  solution. 

Supposing  the  soap  solution  registers  19  milligrammes,  then  it  is  too 
strong,  and  must  be  weakened  so  as  to  register  20  parts — i.e.,  if  the  total 
filtered  soap  solution  is  990  c.c,  it  must  be  made  up  to  ta  of  990  c.c.= 
1,042  c.c.  with  extra  water  and  rectified  spirit. 

The  rationale  of  the  process  is  as  follows:  The  soap  employed 
is  a  combination  of  an  alkali  with  a  fatty  acid.  When  it  is  added 
to  water  which  contains  calcium  and  magnesium  salts  in  solution, 
then  the  fatty  acids  (oleic  mainly  in  this  case)  will  combine  with 
the  lime  and  magnesia  to  form  insoluble  calcic  and  magnesic 
oleate;  and  when  the  soap  is  added  until  there  is  no  longer  any 
lime  and  magnesia  left  to  combine  with,  the  fatty  acids  remain- 
ing in  solution  form  a  lather  on  shaking.  Hence  the  more  cal- 
cium and  magnesium  salts  present,  the  larger  the  amount  of  soap 


40  LABORATORY   WORK 

solution  required,  and,  in  consequence,  the  longer  is  the  produc- 
tion of  a  lather  delayed. 

1.  One  hundred  c.c.  of  the  water  are  placed  \\dthin  the  small 
glass-stoppered  bottle. 

2.  A  graduated  burette  is  then  filled  up  to  the  lo  c.c.  mark 
with  the  soap  solution,  of  which  2  c.c.  are  run  into  the  bottle, 
when  a  cloudy  precipitate  of  insoluble  calcic  and  magnesic  oleate, 
etc.,  is  formed.  The  bottle  is  then  briskly  shaken  to  see  if  its 
contents  will  produce  a  lather. 

3.  The  solution  is  afterwards  added  in  cubic  centimetres,  and 
the  bottle  well  shaken  up  after  each  fresh  addition,  until  even- 
tually a  certain  definite  amount  of  lather  forms.  The  air  should 
be  sucked  from  the  bottle  (with  a  glass  tube)  from  time  to  time, 
so  as  to  remove  any  carbonic  acid  which  has  been  liberated. 
Sufficient  soap  solution  has  been  added  when,  with  the  bottle 
placed  on  its  side,  the  lather  presents  a  thin,  unbroken  surface 
after  the  lapse  of  five  minutes.  It  is  helpful  to  know  that  when 
the  requisite  quantitj^  of  soap  solution  has  been  added,  the  con- 
tents of  the  bottle  on  being  shaken  give  only  a  faint,  dull,  soft 
sound;  and,  after  shaking,  small  particles  of  the  lather  cling  to 
and  slowly  descend  the  sides  of  the  bottle. 

4.  From  the  number  of  cubic  centimetres  of  soap  solution 
required,  the  amount  of  calcium  carbonate,  or  its  equivalent  (in 
soap-destroying  power),  in  the  100  c.c.  of  water,  is  ascertained. 
But  a  deduction  of  i  c.c.  from  the  amount  of  soap  solution  used 
must  be  made  in  every  case,  since  this  amount  is  required  to 
create  a  similar  lather  in  the  same  bulk  of  distilled  water — which 
is  free  from  an}'  of  the  ingredients  which  are  considered  as 
furnishing  "  hardness." 

Example. — One  hundred  c.c.  of  water  required  15  c.c.  of  the 
soap  solution  to  furnish  the  characteristic  lather. 

Deduct  the  i  c.c.  which  would  be  required  for  100  c.c.  of  dis- 
tilled water,  and  14  c.c.  of  soap  solution  indicate  the  total  hardness. 

But  I  c.c.  of  the  soap  solution  =1  milligramme  of  calcium 
carbonate,  or  its  equivalent. 

Therefore  14  c.c.  =  14  milligrammes  of  calcium  carbonate,  or 
its  equivalent. 

Therefore  the  "  total  hardness  "  in  100  c.c.  of  the  water  is 
equivalent  to  14  milligrammes  of  calcium  carbonate;  and  14  milli- 
grammes in  100  c.c.  (or  100,000  milligrammes  of  water)  =  14  parts 
per  100,000. 


HARDNESS  4^ 

Conclusions  to  he  Drawn  from  the  Amount  Estimated. — If  the 
"  total  hardness  "  of  a  water  reaches  30  parts  per  100,000,  it 
becomes  unsuitable  for  washing  and  cooking  purposes;  and  if  it 
reaches  40  it  is  practically  useless  in  these  respects.  A  "  soft  " 
water  may  contain  up  to  10;  a  "  hard  "  water  from  15  to  25;  a 
"  very  hard  "  water  from  30  and  upwards. 

Notes. — Where  the  hardness  exceeds  25  parts  per  100,000,  so 
much  precipitate  of  calcic  and  magnesic  oleate,  etc.,  is  created 
that  it  interferes  with  the  formation  of  a  characteristic  lather, 
and  leads  to  an  error  of  overestimation  of  the  "  hardness."  In 
these  cases  it  is  necessary  to  dilute  the  water  with  an  equal 
amount  of  distilled  water — i.e.,  50  c.c.  of  distilled  water  are 
added  to  50  c.c.  of  the  sample,  and  in  the  estimation  of  the 
hardness  i  c.c.  is  still  deducted  from  the  soap  solution  used. 

When  the  results  are  expressed  in  "  degrees  "  upon  Clark's 
scale,  1°  (Clark)  is  equivalent  i.n  this  country  to  i  grain  of  calcium 
carbonate  per  gallon — i.e.,  to  i  part  per  70,000.  In  France, 
however,  a  degree  signifies  i  part  of  calcium  carbonate  in  100,000 
and  in  Germany  i  part  of  lime  in  100,000. 

The  "  total  hardness  "  having  been  found,  the  next  step  is  to 
ascertain  the  "  temporary  "  and  the  "  permanent  "  hardness. 

1.  One  hundred  c.c.  of  the  water  are  measured  out  and  poured 
into  a  glass  beaker,  which  is  placed  on  an  iron  tripod.  To  protect 
the  glass  against  direct  contact  with  the  flame,  the  beaker  is 
placed  upon  a  triangle  hned  with  pipeclay,  which  itself  rests 
upon  a  piece  of  iron  gauze.  The  water  is  boiled  until  only  about 
two-thirds  of  its  original  volume  remain. 

2.  The  mouth  of  the  flask  is  covered,  and  its  contents  allowed 
to  cool,  when  all  the  calcium  and  magnesium  carbonate,  and 
often  the  bulk  of  any  iron  present,  will  be  contained  in  the  pre- 
cipitate noticeable  at  the  bottom  of  the  beaker.  It  is  the  super- 
natant fluid  which  contains  the  "  permanent  hardness,"  the 
"  temporary  hardness  "  which  has  been  separated  being  repre- 
sented by  the  deposit. 

3.  From  the  beaker  the  cooled  water  is  decanted  into  the 
measuring  flask,  care  being  taken  to  disturb  the  precipitate 
(which  is  left  behind)  as  little  as  possible.  The  water  is  then 
made  up  to  its  original  bulk  by  filling  up  to  the  100  c.c.  mark 
with  recently  boiled  distilled  water;  or  a  reflux  condenser  may 
be  used  while  the  water  is  boiling. 

4.  The  100  c.c.  of  water  is  then  filtered  through  a  fine  filter- 


42  LABORATORY   WORK 

paper  and  its  "  hardness  "  is  estimated  as  previously  described, 
and  the  result  furnishes  the  "  permanent  hardness." 

5.  If  the  "  permanent  hardness  "  be  subtracted  from  the 
"  total,"  the  difference  will  represent  the  hardness  separated 
by  the  boiling — i.e.,  the  "  temporary  hardness." 

Assuming  that  the  permanent  hardness  is  represented  by 
(7-  i)  6  c.c.  of  the  soap  solution,  it  is  thus  equivalent  to  6  parts 
per  100,000  CaCOg. 

The  total  hardness  was  14  parts  per  100,000;  .-.  the  "tem- 
porary hardness"  =1^  —  6,  or  8  parts  per  100,000  of  CaCOg,  or 
its  equivalent. 

Notes. — If  it  is  desired  to  know  the  proportion  of  hardness  due 
to  magnesium  salts  in  a  water,  where  the  "  total  hardness  "  is 
known  to  be  due  entirely  to  calcium  and  magnesium  salts,  it  is 
necessary  to  first  precipitate  and  remove  all  the  calcium  salts  in 
the  manner  described  in  Chapter  VI.,  when  the  hardness  remain- 
ing will  be  due  to  magnesium  salts. 

Wanklyn  has  pointed  out  that  whereas  lime  reacts  imme- 
diately upon  the  solution  of  soap,  magnesia  requires  the  lapse  of 
time;  and  that  one  equivalent  of  magnesia  consumes  as  much 
soap  solution  as  one  and  a  half  of  lime. 

If  magnesium  salts  contribute  materially  to  the  hardness,  a 
thin,  fine,  dirty  scum,  somewhat  similar  to  a  lather,  forms  upon 
the  surface  of  the  water  as  the  soap  solution  is  added.  This  scum 
finally  breaks  up,  and  is  replaced  by  the  genuine  pure  white 
lather.  In  such  cases  the  water  must  be  diluted  considerably 
with  distilled  wate..  Bearing  in  mind  the  longer  time  taken 
for  magnesia  to  react,  the  presence  of  this  film  or  scum  will 
warn  the  operator  that  as  he  adds  the  soap  solution  he  must 
proceed  slowly  and  shake  thoroughly. 

In  Clark's  softening  process  lime  is  added,  in  quantity  depend- 
ing upon  the  amount  of  carbonic  acid  in  the  water,  in  order  that 
it  may  combine  with  this  acid  which  holds  the  calcium  and  mag- 
nesium carbonates  in  solution  (CaC03,C02  +  CaH202=2CaC03 
+  H2O).  When  the  lime  is  added  in  excess,  some  of  it  remains 
in  solution  in  the  water  in  an  uncombined  state,  and  since  this  is 
undesirable  in  drinking-water,  a  water  treated  by  Clark's  process 
should  be  frequently  tested  for  uncombined  Hme.  A  ready  and 
simple  method  of  detection  is  by  adding  a  few  drops  of  a  solution 
of  silver  nitrate  to  some  of  the  water,  when,  if  free  lime  be 
present,  the  cloudiness  created,  instead  of  being  white  and  clean 


HARDNESS  43 

(silver  chloride),  becomes  dirty  and  brown  (an  oxide  of  silver 
being  formed). 

The  Rivers  Pollution  Commissioners  in  their  Sixth  Report 
give  the  following  classification  of  waters  as  to  their  softness: 
(i)  Rain  water;  (2)  upland  surface  water;  (3)  surface  water  from 
cultivated  land;  (4)  river  water;  (5)  spring  water;  (6)  deep- well 
water;  (7)  shallow- well  water;  and  they  found  that  the  follow- 
ing formations  almost  invariably  furnish  hard  waters:  (i)  Cal- 
careous Silurian;  (2)  calcareous  Devonian;  (3)  mountain  lime- 
stone; (4)  calcareous  rocks  of  the  coal-measures;  (5)  new  red 
sandstone;  (6)  conglomerate  sandstone;  (7)  lias;  (8)  oohte; 
(9)  upper  greensand;  (10)  chalk. 


CHAPTER  V 

THE  POISONOUS  METALS 

Those  poisonous  metals  for  which  it  is  commonly  necessary  to 
test  a  water  are  lead,  iron,  and  zinc. 

Water  most  generally  takes  up  these  metals  either  from  pipes 
through  which  it  has  been  made  to  flow,  from  receptacles  in 
which  it  has  been  stored,  or  from  materials  used  in  making  or 
repairing  the  joints  of  pipes  or  cisterns;  but,  in  addition,  such 
metals  may  gain  access  from  trade  processes  carried  on  by  river- 
sides, or  from  metalliferous  mines  within  the  district,  or,  in  the 
case  of  iron,  from  ferruginous  soil  or  strata. 

Lead  may  be  taken  up  from  the  pipes  and  cisterns  made  of 
this  material.  The  action  of  water  upon  this  metal  is  primarily 
an  oxidizing  one,  and  in  the  presence  of  dissolved  oxygen  a  loose 
coating  of  oxj^hydrate  of  lead  may  form.  The  lead  oxide  is 
practically  insoluble  in  those  waters  which  do  noi  contain  some 
free  acid,  but  when  this  is  the  case  (as  notably  in  peaty  waters 
and  those  containing  much  free  COg)  the  lead  salt  is  carried  away 
in  solution ;  in  other  cases  a  relatively  small  quantity  is  removed 
in  suspension.  Ackroyd  finds  that  plumbism  due  to  the  solvent 
action  of  peat}^  waters  does  not  occur  when  the  acidity  of  the 
water  is  equivalent  to  less  than  o"5  part  of  sulphuric  acid  in 
100,000  parts  of  water  (phenolphthalein  being  used  as  indicator). 

Plumbo-solvency  is  diminished  by  the  presence  of  carbonates, 
sulphates,  and  chlorides  in  water  which  is  not  acid,  but  nitrates 
favour  the  oxidation  of  the  metal  to  oxyhydrate.  The  action  of 
the  above  salts  is  ascribed  to  the  varying  solubility  of  the  lead 
salts  of  the  corresponding  acids,  the  nitrate  being  the  most 
soluble,  and  the  sulphate  and  carbonate  the  least  so.  Since  non- 
acid  waters  containing  carbonate  of  calcium  provide  a  coating  of 
carbonate  of  lead  to  the  surface  of  the  metal,  and  this  coating  is 
insoluble  in  such  waters,  unless  there  is  free  COg  over  and  above 

44 


THE    POISONOUS    METALS  45 

the  amount  necessary  to  form  bicarbonate,  it  follows  that  soft 
waters  are  the  great  lead-carriers.  Soluble  phosphates  in  the 
water  will  also  protect  the  metal  to  a  marked  degree.  As  a 
general  rule,  then,  soft  waters  attack  and  hard  waters  protect 
lead;  but  in  certain  districts  hard  waters  containing  free  COg,  but 
a  small  amount  of  carbonate,  are  capable  of  dissolving  appreci- 
able amounts  of  lead. 

"  Soda-water  "  is  particularly  liable  to  take  up  large  quantities 
of  lead  if  it  is  allowed  to  come  into  contact  with  that  metal. 

Waters  containing  a  mere  trace  of  lead  often  present  to  the 
trained  eye  a  faint  haziness.   This  disappears  on  adding  nitric  acid. 

Iron. — A  chalybeate  water  generally  contains  its  iron  in  the 
form  of  ferrous  carbonate  held  in  solution  by  an  excess  of 
carbonic  acid;  on  prolonged  exposure  to  air,  or  by  apply- 
ing heat,  hydrated  ferric  oxide,  or  "  rust,"  is  thrown  down 
(4FeC03  +  02  +  2H20=2Fe203H20-f  4CO2),  since  it  is  insoluble 
in  water  containing  no  free  acid.  Upland,  moorland  and  some 
other  waters  (as  those  from  the  greensand  and  new  red  sand- 
stone) generally  contain  traces  of  iron,  which  are  taken  up  from 
the  soil  or  strata  permeated. 

The  solution  of  iron  from  soils  is  generally  due  to  organic 
matter  removing  oxygen,  and  thus  converting  the  iron  to  the 
ferrous  condition,  in  which  form  it  is  soluble  in  water  containing 
carbonic  acid. 

Copper  is  rarely  found  in  drinking-water;  but  it  is  sometimes 
given  to  water  by  culinary  utensils  made  of  this  metal,  for  a 
small  amount  of  copper  is  dissolved  when  water  which  contains 
common  salt,  acid  (vinegar,  etc.),  fatty  or  oily  material,  is  boiled 
in  contact  with  it.  The  writer  has  recorded  an  instance  where 
the  practice  of  placing  a  penny  into  the  saucepan  in  which 
vegetables  are  boiled,  in  order  to  improve  their  colour,  gave  rise 
to  symptoms  of  copper-poisoning  in  two  children  of  a  household. 
Zine  is  most  generally  taken  up  from  galvanized  iron  cisterns 
and  pipes  or  zinc  surfaces.  All  kinds  of  water  attack  zinc  in  the 
presence  of  air ;  even  hard  waters  with  an  alkaline  reaction.  But 
it  generally  exists  in  water  in  the  form  of  carbonate  held  in  solu- 
tion by  COg,  and  is  not  present  in  more  than  traces,  except  in  soft 
acid  waters.  Galvanized  iron  must  not  be  held  to  entail  danger 
in  its  use,  unless  the  water  contains  much  free  carbonic  acid, 
since  under  common  conditions  the  zinc  oxide  or  basic  carbonate 
form  and  protect  the  metal  from  further  action.     Zinc,  as  sul- 


46  LABORATORY   WORK 

phate,  has  been  observed  in  considerable  quantit}'  in  certain 
springs  in  the  South  of  France,  New  Zealand,  and  America. 

Chromium. — Chromium  may  possibly  get  into  water  from 
colour  and  dye  works,  etc.,  but  it  is  extremely  rare  that  this 
very  poisonous  metal  ever  gains  access  to  drinking-water. 

Tin,  arsenic,  and  barium  are  rarely  found  in  water;  but  man- 
ganese is  not  uncommonly  found  in  some  parts  of  the  Continent. 

Qualitative  Tests  and  Quantitative  Estimation. 
Special  Apparatus  required : 

White  porcelain  basins. 

Boiling  flask. 

Burette  with  c.c.'s  graduated  to  tenths  of  c.c. 

Nessler  glasses. 

Filtering  apparatus. 

Ignition  crucible  and  crucible  tongs. 

Desiccator. 

Drying  oven. 

Chemical  balances. 

Wash-bottle. 

Marsh's  apparatus. 

Special  Reagents  required : 

1.  A  standard  solution  of  lead  acetate — i  c.c.  =  i  milligramme  of  lead — 
made  by  dissolving  1-83  grammes  of  crystallized  acetate  of  lead  in  a  litre 
of  distilled  water. 

2.  A  standard  solution  of  copper  sulphate — i  c.c.  =  i  milligramme  of 
copper — made  by  dissolving  3*927  grammes  of  sulphate  of  copper  in  a  litre 
of  distilled  water. 

3.  A  standard  solution  of  ferric  chloride — i  c.c.=  i  milligramme  of  iron 
— made  by  dissolving  1-004  grammes  of  iron  wire  in  nitro-hydrochloric 
acid,  precipitating  with  ammonia  solution,  washing  and  redissolving  the 
ferric  oxide  in  a  little  hydrochloric  acid,  and  then  diluting  to  a  litre. 

Each  of  these  standard  solutions  may  be  diluted,  in  some  cases  with 
advantage,  so  that  each  c.c.  contains  o-i  milligramme  of  the  metal. 

Solutions  of — 

Ammonium  sulphide. 

Cyanide  of  potassium. 

Ferrocyanide  of  potassium. 

Yellow  chromate  of  potassium. 

Ammonia. 

Ammonium  chloride. 

Mercuric  chloride. 

Peroxide  of  hydrogen. 

Dilute  hydrochloric  acid. 

Solid  potassium  nitrate  and  sodium  carbonate. 

Granulated  zinc. 

Metallic  copper. 


THE    POISONOUS   METALS  47 

Qualitative  Tests. 

Though  the  metals  lead,  copper,  and  iron,  even  when  existing 
in  faint  traces,  may  generally  be  detected  by  testing  the  original 
water,  it  is  sometimes  desirable  to  reduce  the  bulk  of  the  water — 
and  thus  concentrate  their  solutions,  as  it  were — by  evaporation 
before  testing.  In  the  case  of  zinc,  it  will  always  be  necessary 
to  thus  considerably  reduce  the  original  bulk  of  the  water.  A 
litre  of  water  may  be  evaporated  to  200  c.c.  by  previously 
marking  a  narrow  beaker  at  the  precise  level  to  which  200  c.c. 
of  water  reaches,  and,  after  acidulating  with  a  drop  or  two  of 
hydrochloric  acid,  in  order  to  keep  the  metals  in  solution,*  boil- 
ing the  litre  of  water  until  it  is  reduced  to  this  level. 

Lead,  Copper,  and  Iron. — i.  To  about  loo  c.c.  of  the  sample 
of  water,  placed  in  a  white  porcelain  dish,  apply  a  little  of 
the  ammonium  sulphide  solution  by  means  of  a  glass  rod  which 
has  been  dipped  in  the  solution.  By  drawing  the  rod  gently 
through  the  water,  and  noticing  any  discoloured  streak  imme- 
diately adjacent  to  the  track  of  the  rod,  faint  quantities  of  poison- 
ous metals  will  be  more  readily  detected  than  by  allowing  a  drop  of 
the  reagent  to  fall  into  the  water  and  then  stirring.  The  reason 
for  this  is  that  the  reagent  itself  imparts  a  slight  colour,  and  it  is 
therefore  advisable  to  add  as  little  of  it  as  possible  to  commence 
with,  otherwise  a  faint  discoloration  caused  by  a  metal  may  be 
lost  in  that  created  by  the  reagent. 

Any  evidence  of  a  dark  colour  appearing  in  the  water  denotes 
the  formation  of  the  sulphides  of  either  lead,  iron,  or  copper, 
and  the  ammonium  sulphide  should  then  be  further  added  until 
the  maximum  amount  of  darkening  has  been  produced.  It 
must  be  borne  in  mind  that  iron  when  in  faint  traces  may  only 
impart  a  slight  dirty  green  colour  to  ammonium  sulphide  at 
first,  but  after  a  while  the  black  colour  of  the  sulphide  forms. 

If  there  is  any  colour  present  in  the  original  water,  a  com- 
parison must  be  made  with  a  similar  quantity  of  the  water  placed 
in  another  porcelain  dish,  before  it  is  decided  whether  any 
additional  colour  has  been  furnished  by  the  ammonium  sulphide. 
Where,  however,  the  colour  originally  present  is  marked  (as  by 
peat,  etc.),  it  may  well  obscure,  even  with  these  precautions,  a 
trace  of  lead,  iron,  or  copper.  It  must  then  be  decolorized  as 
follows :  100  c.c.  are  acidiiied  with  hydrochloric  acid  and  heated  to 
*  If  the  presence  of  lead  is  suspected,  the  water  should  not  be  acidulated. 


48  LABORATORY   WORK 

boiling;  a  crystal  of  sodium  chlorate  is  added  to  the  liquid,  which 
is  next  boiled  until  the  excess  of  chlorine  is  expelled.  Ammonia 
is  then  added  to  the  cold  solution  until  it  is  just  alkaline,  and 
the  whole  diluted  to  its  original  volume  with  distilled  water. 

2.  If  the  water  darkens,  pour  half  of  it  into  a  second  porcelain 
dish.  To  one  part  add  a  drop  or  two  of  dilute  hydrochloric  acid, 
when  if  the  colour  disappears  it  is  due  to  iron  ;  or  if  it  diminishes 
perceptibly  iron  is  present. 

3.  A  confirmatory  test  should  then  be  applied  to  some  of  the 
water  in  a  test-tube — i.e.,  a  drop  or  two  of  HCl  is  followed  by  a 
few  drops  of  a  solution  of  the  ferroc^^anide  of  potassium,  when 
the  colour  of  Prussian  blue  (ferrocyanide  of  iron)  is  produced. 
Another  very  delicate  test  is  to  boil  the  water  with  a  few  drops  of 
nitric  acid,  cool,  and  add  a  little  potassium  sulphocyanide;  when 
a  blood-red  or  sherry  colour  results,  due  to  ferric  sulphocyanide. 

4.  If,  after  adding  the  hydrochloric  acid,  the  colour  does  noi 
disappear,  the  metal  is  either  lead  or  copper.  To  the  other  half 
of  the  darkened  water  add  a  few  drops  of  a  solution  of  potassium 
cyanide;  the  PbS  will  be  unaffected,  but  CuS  will  be  completely 
dissolved. 

An  excellent  conlirmator}^  test  for  lead  is  to  add  to  some  of 
the  water  in  a  test-tube  a  few  drops  of  a  solution  of  the  yellow 
chromate  of  potassium,  when  if  lead  is  present  an  opacity 
appears  in  the  water  (due  to  the  formation  of  lead  chromate). 
The  reaction,  is,  however,  difficult  of  appreciation  with  faint 
traces  of  lead,  which  will  often  be  missed  by  this  test  unless  a 
careful  comparison  is  instituted  with  another  test-tube  containing 
a  similar  amount  of  lead-free  water  and  reagent. 

Iron  may  possibly  be  present  along  with  lead,  and  may  con- 
tribute to  the  darkening  created  by  the  ammonium  sulphide.  If 
so,  this  may  be  detected  by  adding  a  drop  of  dilute  hydrochloric 
acid  to  the  water,  for  this  has  been  seen  to  remove  any  darkening 
furnished  by  an  iron  salt.  Or  the  iron  may  be  separated  by 
adding  nitric  acid,  evaporating  to  a  small  bulk,  and  precipitating 
the  iron  with  excess  of  ammonia  and  warming;  the  precipitate 
of  ferric  oxide  may  be  separated  on  a  ftlter-paper,  washed,  dis- 
solved in  nitric  acid,  then  reprecipitated  with  ammonia,  and 
again  filtered  and  washed;  the  filtrate  should  be  boiled  until 
the  ammonia  is  driven  oft",  and  then  tested  for  lead. 

5.  As  a  confirmatory  test  for  copper,  a  drop  or  two  of  a  solu- 
tion of  the  ferrocyanide  of  potassium  should  be  added  to  some 


THE   POISONOUS   METALS  49 

of  the  water  after  it  has  been  acidulated  with  a  drop  of  dihite 
hydrochloric  acid.  If  copper  is  present,  a  bronze  coloration  and 
precipitate  of  cupric  ferrocyanide  appears. 

A  faint  colour  will  often  be  missed,  unless  it  be  looked  for 
through  the  depth  of  the  water  on  to  a  white  background. 

6.  When  no  darkness  is  created  and  it  is  judged  desirable  to 
test  for  zinc,  concentrate  the  water;  render  slightly  alkaline 
with  ammonia ;  add  a  few  drops  of  ammonium  chloride  solution ; 
then  boil;  add  to  some  of  the  further  concentrated  water,  after 
filtration,  a  few  drops  of  ammonium  sulphide.  The  white  pre- 
cipitate (of  hydrated  sulphide)  formed  in  the  presence  of  zinc 
when  once  seen  will  always  be  recognized,  since  it  is  of  a  floc- 
culent,  curdled,  or  gelatinous  nature. 

As  a  confirmatory  test,  render  the  water  slightly  alkaline 
with  ammonia;  further  concentrate  by  boiling;  filter;  add  a  few 
drops  of  the  ferrocyanide  of  potassium  with  excess  of  dilute 
hydrochloric  acid,  and  note  a  white  gelatinous  precipitate  of  zinc 
ferrocyanide,  insoluble  in  dilute  acids.  Potassium  ferricyanide 
furnishes  a  rusty  yellow  precipitate  of  zinc  ferricyanide,  soluble 
in  hydrochloric  acid  and  ammonia. 

7.  The  presence  of  arsenic  has  extremely  rarely  to  be  tested 
for,  but  when  it  is  desirable  to  do  so  Marsh's  test  is  the  most 
delicate. 

A  litre  of  water  is  rendered  alkaline  by  solid  sodium  carbonate 
(free  from  arsenic);  evaporated  nearly  to  dryness;  and  the 
residue  introduced  into  Marsh's  apparatus.  For  a  full  description 
of  the  application  of  Marsh's  process,  see  "Arsenic  in  Food." 

8.  Tin. — A  litre  of  water  should  be  evaporated  to  a  solid 
residue,  and  the  tin  dissolved  out  from  the  ash  by  warming  mth 
a  little  strong  hydrochloric  acid ;  then  dilute  a  little  and  boil  for 
a  long  time  with  metallic  copper  to  make  certain  that  the  tin 
exists  in  a  stannous  condition;  decant  and  add  excess  of  a  solu- 
tion of  mercuric  chloride,  when  a  silky-looking  cloud  of  mercurous 
chloride  appears  (2HgCl2  +  SnCl2=  SnCl4  +  2HgCl).  If  a  mixture 
of  ferricyanide  of  potassium  and  ferric  chloride  be  added  to  a 
solution  containing  stannous  oxide  or  chloride  and  hydrochloric 
acid,  a  precipitate  of  Prussian  blue  results  from  the  reduction  of 
the  ferri-  to  the  ferro-cyanide.  If  no  other  reducing  agents  are 
present,  this  is  very  delicate.  Sulphuretted  hydrogen  yields  a 
dark  brown  precipitate  with  stannous  salts,  soluble  in  potassic 
hydrate. 


50  .LABORATORY   WORK 

9.  Chromium. — A  good  test  is  to  collect  the  residue  from  a 
litre  of  water:  fuse  the  ash  with  solid  potassium  nitrate  and 
sodium  carbonate,  so  as  to  produce  the  yellow  chromate  of 
potassium;  tliis  in  a  neutral  solution  yields  a  purple  precipitate 
with  excess  of  silver  nitrate.  Slight  traces  may  be  detected  by 
concentrating  the  water  to  a  very  small  bulk,  and  then  letting 
it  drop  upon  a  thin  layer  of  ether  floated  on  a  dilute  solution  of 
peroxide  of  hydrogen  acidified  with  sulphuric  acid;  the  blue 
colour  that  forms  in  the  lower  solution  passes  over  to  the  ether 
upon  slight  agitation. 

10.  Manganese. — Occasionally  this  metal  is  found  in  water, 
and  its  presence  has  been  noted  more  particularly  in  America 
and  German^^  A  delicate  test  (Wanklj-n)  is  to  evaporate  a  litre 
of  water  to  a  small  bulk;  nearly  neutralize  with  hydrochloric 
acid;  and  treat  with  a  few  drops  of  peroxide  of  hj'drogen  solution, 
when  a  brown  precipitate  forms  in  the  presence  of  manganese. 

Having  thus  detected  the  presence  of  a  poisonous  metal,  it 
becomes  necessary  to  estimate  its  amount. 

OUAXTITATIVE    ESTIMATION. 

The  estimation  of  lead,  copper,  and  iron  may  be  performed  by 
a  colorimetric  or  colour-matching  process. 

1.  Measure  out  100  c.c.  of  the  concentrated  water  which  has 
been  found  to  contain  lead,  and  pour  into  a  Nessler  glass  (a  glass 
cyhnder  graduated  to  50  c.c). 

2.  Place  a  similar  amount  of  lead-free  water  into  three  other 
Nessler  glasses,  to  which  different  amounts  (from  o-i  to  i-o  c.c.) 
of  a  standard  solution  of  the  metal  have  been  carefully  added. 

3.  To  each  glass  add  one  drop  of  the  ammonium  sulphide 
solution,  and  well  stir  with  a  glass  rod  reserved  for  each  basin. 

4.  Note  which  of  the  standard  waters  forms  a  match  with  the 
water  under  examination,  and  therefore  contains  the  same 
amount  of  Pb. 

Example. — The  amount  of  standard  solution  added  to  the 
particular  100  c.c.  of  distilled  water  which  matched  the  brown 
coloration  in  the  sample  of  lead-polluted  water  was  0*4  c.c. 

But  I  c.c.  =  I  milligramme  of  lead. 

.-.  o"4  c.c.  =  0-4  milligramme  of  lead. 

.-.  there  is  0-4  milligramme  of  lead  in  100  c.c.  of  the  concen- 
trated water. 

But  the  water  was  concentrated  to  one-fifth  of  its  original 


THE    POISONOUS   METALS  51 

bulk;  .-.  the  0-4  milligramme  of  lead  represents  0*08  milligramme 
in  100  CO.  of  the  original  water,  or  o-o8  part  per  100,000, 
or  0-056  grain  per  gallon  (about  y\  grain).  It  is  often  better  to 
work  with  a  weaker  standard  solution  made  up  to  one-tenth  of 
the  strength  of  the  solution  here  referred  to ;  and  as  it  is  only  very 
light  shades  of  brown  which  can  be  matched  with  great  precision, 
if  there  is  much  metal  present  it  may  be  necessary  to  lessen  the 
degree  of  concentration,  or  even  to  deal  with  the  original 
water. 

Similarly,  a  quantitative  estimation  of  copper  and  iron  may  be 
made  by  employing  standard  solutions  of  these  metals. 

Iron  may  be  estimated  gravimetrically,  if  in  appreciable 
amount,  in  the  following  manner,  and  the  colorimetric  estimation 
thereby  checked: 

The  ash  from  the  residue  of  500  c.c.  of  the  water  is  digested  in 
strong  hydrochloric  acid;  after  filtration,  the  filter-paper  and  its 
contents  are  well  washed  with  boihng  distilled  water;  then  add 
two  drops  of  nitric  acid  to  the  filtrate,  boil  and  add  ammonium 
chloride  solution  and  a  slight  excess  of  ammonia.  Collect  the 
precipitate  on  a  Swedish  filter-paper;  wash  with  boiling  water; 
dry  in  hot-air  oven  at  105°  C.  The  filter-paper  should  next  be 
folded  up,  placed  in  a  small  porcelain  crucible  (previously 
weighed)  and  covered  by  a  lid;  then  ignite  to  dull  redness,  at 
first  gently  so  as  to  obviate  spurting  and  loss,  and  the  lid  should 
be  removed  after  a  while  so  as  to  permit  free  access  of  air.  When 
the  filter-paper  has  been  entirely  destroyed,  let  the  capsule  and 
its  contents  cool  under  a  desiccator,  and  weigh.  The  weight 
found,  minus  that  of  the  crucible  and  the  ash  of  the  filter-paper, 
represents  the  weight  of  FegOg,  and  this  x  07  =  Fe. 

The  quantitative  estimation  of  zinc  can  be  conveniently  made, 
gravimetrically,  by  taking  a  measured  quantity  of  the  concen- 
trated water  (which  is  found  to  be  free  from  other  poisonous 
metals)  and  collecting  the  precipitate  of  zinc  sulphide  (obtained 
as  described  above)  on  a  filter;  this  is  then  well  washed  with 
dilute  ammonium  sulphide,  dried,  ignited  in  a  weighed  capsule 
at  a  bright  red  heat,  allowed  to  cool,  and  finally  weighed  as 
oxide  (ZnO).  The  weight  obtained  x  0-8  =  Zn.  Or  an  approxi- 
mate estimation  may  be  made  by  preparing  a  standard  solution 
of  zinc  (4-4  grammes  of  the  sulphate  to  i  litre  of  water;  i  c.c.  = 
I  milligramme  Zn),  and  matching,  on  the  lines  indicated  above, 
the  turbidity  produced  in  100  c.c.  of  the  concentrated  water 


52  LABORATORY   WORK 

after  a  small  measured  quantity  of  potassium  ferrocyanide  has 
been  added. 

For  the  determination  of  small  quantities  of  manganese  in 
drinking-water,  the  colorimetric  method  of  Volhard  and  Tread- 
well,  modified  for  drinking-water,  is  recommended — that  is, 
oxidation  of  manganese  to  permanganic  acid  \vith  nitric  acid 
and  lead  peroxide,  and  comparison  of  the  coloured  liquid  with 
nitric  acid  solutions  containing  known  amounts  of  permanganate. 

A  very  approximate  quantitative  estimation  may  be  made, 
colorimetrically,  as  follows  (Haas) : 

One  hundred  c.c.  of  the  water  under  examination  are  acidified 
with  5  c.c.  of  20  per  cent,  sulphuric  acid,  i  gramme  of  potassium 
persulphate  is  added,  and  the  solution  is  heated  until  a  reddish- 
violet  coloration  is  obtained,  or  until  a  brown  colour,  due  to 
manganese  dioxide,  develops.  The  solution  is  now  cooled,  a 
trace  of  sodium  hydrogen  sulphite  is  added,  and  the  oxidation 
with  persulphate  is  repeated.  The  coloration  obtained  is  then 
compared  with  that  exhibited  by  j§^  potassium  permanganate 
solution. 

Co7iclusions  to  he  Drawn  from  the  Amount  Estimated. — Opinion 
is  somewhat  divided  as  to  the  amounts  of  the  poisonous  metals 
which  may  be  considered  dangerous  in  drinking-water.  In  the 
case  of  lead,  ^  of  a  grain  to  the  gallon  is  accepted  as  the  limit 
by  many  authorities ;  for  in  the  case  of  a  poisonous  metal  which 
is  cumulative  in  its  action,  a  very  small  trace  should  be  con- 
sidered sufficient  to  render  condemnation  of  the  water  justifiable. 

There  is  evidence  that  the  system  becomes  habituated  to 
copper  salts,  but  this  metal,  if  allowed  at  all,  certainly  never 
ought  to  exceed  yV  grain  to  the  gallon  in  drinking-waters,  for  it 
is  cumulative — though  to  a  less  degree  than  lead. 

Zinc  rarely  exists  but  in  traces;  and  since  it  is  not  a  cumula- 
tive poison,  the  possibihty  of  danger  from  this  metal  is  remote. 

Therefore  with  regard  to  zinc,  a  trace  (not  exceeding  yV  grain 
to  the  gallon)  may  perhaps  be  allowed,  for  waters  containing 
such  a  trace  have  been  drunk  continuously  without  apparent 
harm;  but  the  faintest  trace  of  arsenic — an  exceptionally 
poisonous  and  somewhat  cumulative  metal — would  suffice  to 
condemn  the  water. 

Iron  is  not  harmful  to  the  same  extent;  and  since  it  gives 
indication  of  its  presence  when  in  such  amounts  as  would  make 
its  ingestion  undesirable,  by  imparting  a  distinct  taste  to  the 


THE   POISONOUS   METALS  53 

water,  its  powers  for  evil  are  small;  for  people  will  not,  as  a  rule, 
drink  water  that  is  unpleasant  to  the  palate.  A  quarter  of  a 
grain  per  gallon  is  an  amount  which  is  just  appreciable  by  taste. 

Iron  in  a  general  water-supply  should  under  no  circumstances 
exceed  I  grain  per  gallon,  as  a  slight  excess  of  this  quantity  may 
after  a  time  provoke  dyspepsia,  headache,  etc.,  in  some  people. 

To  determine  the  solvent  action  of  a  particular  water  on  lead 
or  zinc  surfaces,  a  piece  of  the  metal  may  be  submerged  for 
twenty-four  hours  in  a  known  quantity  of  the  water  in 
question. 


CHAPTER  VI 

CALCIUM   AND   MAGNESIUM  SALTS— SILICA— SULPHATES - 
PHOSPHATES 

Special  Reagents  required : 

Solutions  of — ■ 

Ammonium  chloride. 

Ammonia. 

Ammonium  oxalate. 

Sodium  phosphate  (saturated). 

Barium  chloride. 

Hydrochloric  acid. 

Nitric  acid. 

Molyhdic  Solution. — Dissolve  i  part  of  pure  molybdic  acid  in  4  parts  ot 
NH3  (S.G.  0-960);  filter,  and  pour  with  constant  stirring  into  15  parts  of 
nitric  acid  (S.G.  1-2);  let  stand  in  the  dark  for  a  few  days;  carefully 
decant,  and  keep  in  the  dark. 

Magnesium  Mixture. — Fifty-five  grammes  of  crystallized  magnesium 
chloride  are  added  to  70  grammes  of  ammonium  chloride,  and  the  whole 
dissolved  in  i  litre  of  2^  per  cent,  ammonia.  About  15  c.c.  of  the  mixture 
should  be  used  to  precipitate  o-i  gramme  P20g. 

Special  Apparatus  required : 

Filtering  apparatus. 

Platinum  dish. 

Desiccator. 

Ignition  crucible  and  tongs. 

Glass  beakers  and  stirring  rods 

Water-bath  and  drving  oven. 


Calcium  Salts. 

The  presence  of  calcium  salts,  which  mainly  exist  as  the  bicar- 
bonate and  sulphate  in  water,  may  be  indicated  as  follows :  Add 
a  solution  of  ammonium  chloride  and  sufficient  ammonia  to 
furnish  a  slight  ammoniacal  odour.  If  there  is  any  opacity  or 
precipitate  (due  to  ferric  hydroxide,  etc.),  filter;  then  add  am- 
monium oxalate  solution  to  the  filtrate,  when  a  white  precipitate 

54 


MAGNESIUM   SALTS  55 

of  calcium  oxalate  forms.  The  ammonium  chloride  serves  to 
hold  any  magnesium  oxalate  in  solution,  as  soluble  ammonio- 
magnesium  oxalate. 

For  a  quantitative  estimation,  a  measured  quantity  of  water 
(say  200  c.c.  concentrated  from  a  htre  of  water  previously  acidi- 
fied with  a  drop  or  two  of  HCl)  must  be  thus  treated  and  set  aside 
in  a  warm  place  for  several  hours;  the  precipitate  carefully 
filtered  (until  the  filtrate  is  quite  clear)  through  a  Swedish  filter- 
paper;  the  oxalate  of  calcium  precipitate  remaining  on  this 
filter- paper  is  thoroughly  washed,  with  hot  distilled  water,  and 
afterwards  dried  in  the  hot-air  oven  at  a  temperature  of  105°  C. ; 
it  is  then  ignited,  the  capsule  and  its  contents  allowed  to  cool 
under  the  desiccator,  and  the  weight  taken.  The  weight  found, 
minus  that  of  the  crucible  and  the  ash  of  the  filter-paper,  repre- 
sents the  weight  of  the  calcium  as  carbonate — to  which  form  the 
oxalate  has  been  reduced  by  ignition. 

Magnesium  Salts. 

These  generally  exist  in  water  in  the  form  of  the  bi-carbonate 
and  sulphate,  and  chiefly  in  water  collected  from  sandstone 
deposits  in  the  neighbourhood  of  the  coast  and  from  the  dolomite 
strata.  If  these  salts  exceed  10  parts  per  100,000  they  may  cause 
dyspepsia  and  diarrhoea  in  those  unaccustomed  to  the  use  of  such 
waters.  The  presence  of  magnesium  salts  may  be  best  ascer- 
tained by  precipitating  all  the  lime  present  in  the  water  by  means 
of  a  solution  of  ammonium  oxalate,  ammonium  chloride  and 
ammonia;  filtering  until  the  filtrate  is  perfectly  clear  and  free 
from  lime,  as  shown  by  ammonium  oxalate  solution  furnishing 
no  opacity;  the  filtrate,  slightly  acidified  with  hydrochloric 
acid,  should  next  be  concentrated  by  boiling,  and  a  few  drops 
of  a  saturated  solution  of  phosphate  of  sodium  added,  with 
sufficient  ammonia  to  create  strong  alkalinity ;  the  whole  is  well 
stirred  up  with  a  glass  rod  and  then  set  aside  for  several  hours 
when  a  crystalline  precipitate  of  a  double  phosphate  of  magnesium 
and  ammonium  (ammonium-magnesium  phosphate)  is  formed. 

In  those  cases  where  the  magnesium  salts  are  present  only  in 
minute  traces  no  definite  precipitate  results,  but  the  points  where 
the  stirring-rod  has  touched  the  glass  appear  as  white  streaks, 
readily  soluble  in  hydrochloric  acid. 

The  above  precipitate  of  ammonium-magnesium  phosphate 
may  for  the  purpose  of  a  quantitative  estimation  be  collected  on 


56  LABORATORY   WORK 

a  filter ;  washed  with  dilute  ammonia;  dried;  ignited  at  a  red  heat; 
and  weighed  when  cold  as  pyrophosphate  (MgaPaO,),  to  which 
the  red  heat  reduces  the  double  salt.     MggPaO?  x  0-219=  Mg. 

The  amount  present  can  also  be  approximately  estimated  from 
the  hardness  wliich  magnesium  will  create  when  a  water,  pre- 
viously freed  from  calcium  salts,  is  tested  by  the  soap  solution. 
Supposing,  for  instance,  5  c.c.  of  the  soap  solution  are  required 
to  satisf}'  the  hardness  remaining  in  100  c.c.  of  such  water; 
deduct  I  c.c.  (the  amount  of  solution  required  to  produce  a 
similar  lather  in  an  equal  bulk  of  distilled  water)  =  4  c.c. 

But  I  c.c.  of  soap  solution  =  I  milligramme  of  calcium  car- 
bonate. 

.■.4  c.c.  =  4  milligrammes  of  calcium  carbonate. 

.'.  the  hardness  due  to  magnesium  salts  in  100  c.c.  of  water  is 
equivalent  to  4  milhgrammes  of  calcium  carbonate.  But  i  part 
of  calcium  carbonate  is  equivalent  to  0*56  part  of  magnesium 
carbonate  (Wanklyn),  since  i  equivalent  of  magnesia  consumes 
as  much  soap  as  i|  equivalents  of  lime;  for  CaCOg  is  to  MgCOg 
not  as  their  respective  molecular  weights  {i.e.,  100  to  84),  but  as 
150  :  84,  or  as  I  :  0-56. 

.-.  the  magnesium  would  be  equivalent  to  4  x  0-56=  2-24  parts 
of  magnesium  carbonate  in  100,000  of  water,  or  1-56  grains  per 
gallon. 

Magnesium  carbonate  has  been  estimated  as  high  as  9  grains 
per  gallon  by  Wanklyn  and  Playfair,  in  a  Sunderland  water. 

Silica. 

The  estimation  of  silica  may  become  of  importance,  having  in 
view  the  fact  that  its  presence  diminishes  the  plumbo-solvent 
action  of  water. 

For  the  quantitative  estimation  a  measured  quantity  of  water, 
say  500  c.c,  is  slightly  acidulated  with  hydrochloric  acid,  and 
then  evaporated  to  a  solid  residue;  this  is  treated  with  strong 
hydrochloric  acid,  and  afterwards  well  washed  with  boiling 
distilled  water;  the  residue  collected  on  a  filter  is  dried,  ignited, 
and  again  treated  with  the  acid  and  washed  as  before;  any  residue 
ultimately  left  will  consist  of  most,  if  not  all,  of  the  silica  origin- 
ally present  in  the  water,  and  the  white  gritty  powder  of  siUca 
(SiOa)  may  be  dried,  ignited,  and  weighed. 


SULPHATES  57 


Sulphates. 


Sulphates  exist  in  most  waters,  especially  those  which  have 
been  in  contact  with  selenitic*  deposits.  They  are  either  derived 
from  the  soil  or  strata  over  or  through  which  the  water  has  passed, 
or  from  the  sulphur  contained  in  organic  pollution  (urine,  etc.). 
The  rain  water  collected  in  large  towns  yields  small  amounts, 
originally  derived  from  the  sulphur  in  the  coal  burnt.  Sul- 
phates in  water  sometimes  result  from  the  oxidation  of  metallic 
sulphides  (chiefly  iron  pyrites),  which  exist  as  such  in  certain 
deposits.  They  mainly  exist  as  calcium  and  magnesium  sul- 
phates, and  less  generally  as  sodium  sulphate;  and  either  of 
these  salts,  if  present  in-  large  amount,  would  tend  to  cause 
diarrhoea  and  dyspepsia  in  those  unaccustomed  to  the  use  of  the 
water. 

Waters  collected  from  the  limestone  and  dolomite  formations 
always  contain  a  marked  amount  of  sulphates.  The  sulphates 
in  limestone  may  reach  to  20  parts  per  100,000,  and  consist 
mainly  of  calcium  sulphate ;  while  those  in  magnesium  limestones 
and  dolomite  consist  partly  of  magnesium  sulphate.  Chalk 
waters  are  relatively  poor  in  sulphates. 

The  varieties  of  growth  found  capable  of  fixing  sulphur  and 
flourishing  when  sulphuretted  hydrogen  and  sulphates  are 
abundant  in  water  (as  in  the  case  of  gross  sewage  contamination 
and  acid  waste  waters  gaining  access),  are:  Leptomitus  lacteus, 
SphcBrotilus  natans,  Beggiatoa  alba,  and  certain  zooglea  masses 
which  may  assume  a  branching  appearance  and  simulate  the  other 
forms  microscopically.  Each  form  presents  to  the  naked  eye 
the  appearance  of  long  dirty  white  tufts,  which  are  attached  to 
stones,  etc.,  in  the  bed  and  on  the  banks  of  streams  below  the 
level  to  which  the  water  reaches. 

Qualitative  Test.— To  some  of  the  water  previousl3/  acidified 
with  dilute  HCl  and  placed  in  a  test-tube,  a  few  drops  of  chloride 
of  barium  solution  are  added;  this  is  then  left  to  stand  for  a 
few  minutes,  when  an  opacity  or  precipitate  of  the  sulphate  of 
barium  is  created  with  even  very  small  quantities  of  sulphates. 
(H2S04+BaCl2=BaS04  +  2HCl.) 

For  the  quantitative  estimation,  100  c.c.  of  water  (concentrated 
from  a  litre)  should  be  strongly  acidified  with  hydrochloric  acid, 
heated  to  boiling,  and  an  excess  of  a  hot  3  per  cent,  solution  of 

*  Selenite  is  a  natural  foliated  or  crystallized  sulphate  of  lime 


58  LABORATORY   WORK 

barium  chloride  cautiously  added,  with  constant  stirring,  until 
the  maximum  turbidity  is  furnished;  the  precipitate  formed  is 
collected  on  a  small  Swedish  filter-paper,  washed,  ignited  at  a 
moderate  red  heat,  and  weighed  as  barium  sulphate;  the  washing 
of  the  precipitate  is  continued  until  the  filtrate  no  longer  gives  a 
turbidity  with  silver  nitrate. 

If  there  is  any  doubt  as  to  whether  sufficient  of  the  barium 
chloride  solution  has  been  added,  let  stand  until  the  barium 
sulphate  has  settled,  then  add  more  barium  chloride  solution  to 
the  clear  supernatant  water,  and  note  if  any  further  turbidity 
occurs.     If  not,  sufficient  has  been  added. 

To  express  the  result  in  terms  of  sulphuric  acid  (SO3)  it  is  neces- 
sary to  multiply  the  weight  of  barium  sulphate  by  0'343.  In 
drinking-waters  the  amount  of  SO3,  as  sulphates  of  the  alkalies 
and  of  magnesium,  should  not  exceed  10  parts  per  100,000. 

Phosphates. 

The  phosphates  found  in  water  are  commonly  those  of  potas- 
sium, sodium,  and  ammonium,  and  their  double  salts.  Their 
presence  affords  corroborative  evidence  of  animal  contamination 
(especially  urine) ;  but  they  may  only  exist  in  small  amounts  in 
waters  dangerously  polluted,  for  phosphoric  acid  is  eagerly 
retained  by  the  soil  which  the  water  may  have  subsequently 
come  in  contact  with.  When  this  point  is  considered  in  con- 
junction with  the  facts  that  traces  of  phosphates  may  also  have 
their  origin  in  strata — chiefly  sandstone — permeated,  and  that 
they  have  also  been  found  to  be  present  in  some  marshy  waters 
unpolluted  with  animal  matter,  it  will  be  realized  that  they  do 
not  often  furnish  evidence  of  value  to  the  analyst.  But  when  in 
marked  amount  they  may  be  taken  as  a  certain  sign  of 
dangerous  organic  pollution.  Their  complete  absence,  on  the 
other  hand,  is  no  guarantee  of  a  water's  freedom  from  such 
pollution. 

In  every  case  before  a  test  is  applied  for  phosphates  the  water 
should  be  reduced  from  a  large  bulk  to  a  ver}^  small  one  by 
evaporation,  and  it  is  even  preferable  to  dissolve  the  phosphates 
out  from  the  ash  of  the  water. 

Qualitative  Test. — Five  hundred  c.c.  of  water  are  acidified  with 
a  little  nitric  acid  and  evaporated  to  a  solid  residue ;  the  residue 
is  dried  over  a  water-oven  for  two  hours,  to  render  any  silica 


PHOSPHATES  59 

insoluble;  then  dissolve  in  3  c.c.  of  dilute  nitric  acid  and  filter; 
mix  the  filtrate  with  3  c.c.  of  molybdic  solution,  gently  warm, 
and  set  aside  for  fifteen  minutes  at  a  temperature  of  about 
26°  C.  If  "  traces  "  of  phosphates  are  present,  a  faint  greenish- 
yellow  turbidity  will  be  noted;  if  "heavy"  traces,  a  marked 
yellow  precipitate  falls. 

The  quantitative  estimation  may  be  made  by  comparing  the 
colour  results  obtained,  with  standards  made  by  diluting  vary- 
ing quantities  of  a  standard  solution  of  sodium  phosphate 
(i  c.c.  :=o-i  milligramme  of  P2O5);  or  if  the  precipitate  (which 
consists  of  yellow  phospho-molybdate)  is  appreciable,  it  may  be 
collected  from  500  c.c.  of  water,  washed  with  distilled  water, 
dissolved  in  ammonia,  and  precipitated  with  magnesium  mixture. 
This  precipitate  is  then  collected  and  washed  with  2|  per  cent, 
ammonia,  ignited,  and  weighed  as  MgaPgO,  (magnesium  pyro- 
phosphate). The  MggPaOy  X  0-64=  P2O5.  If  this  is  the  amount 
in  500  c.c,  of  water,  one-fifth  of  this  will  represent  parts 
per  100,000. 

More  than  0-05  part  of  P2O5  per  100,000  should  always  be 
regarded  with  suspicion  (Hehner). 


CHAPTER  VII 
THE  SOLID  RESIDUE 

Special  Apparatus  required  : 

Water-bath. 
Platinum  dish. 
Drying  oven. 
Crucible-tongs. 
Chemical  balances. 

By  "  the  solid  residue  "  of  water  is  generally  implied  the  sub- 
stances which  are  held  in  solution,  and  which,  when  the  water  is 
evaporated  to  dryness,  remain  behind;  and  such  a  significance 
must  be  attached  to  the  expression  "  total  sohds  "  throughout 
Part  I.  of  this  book. 

The  solubility  of  much  of  the  matter  taken  up  by  water  may 
be  determined  by  soil  micro-organisms,  and  the  amount  of  sohd 
matter  in  water  collected  from  a  depth  will  depend  upon  the 
geological  characters  of  the  locality  from  which  it  has  been 
collected. 

The  Process. 

The  suspended  matters  are  first  allowed  to  subside,  or  are 
separated  by  filtration  either  through  a  clean  porcelain  filter  or 
through  several  large  filter-papers,  ribbed,  and  packed  rather 
loosely  into  a  large  funnel.  These  filter-papers  must  be  pre- 
viously well  washed  with  distilled  water. 

1.  Fifty  c.c.  of  the  water  are  placed  in  a  previously  weighed 
platinum  dish;  this  is  then  put  upon  the  water-bath,  and  it  may 
be  protected  from  dust  by  means  of  a  small  glass  cover,  one  side 
of  which  is  raised  a  little  by  inserting  a  glass  rod  beneath  it,  so  as 
to  allow  the  condensed  moisture  to  escape. 

2.  When  the  water  is  evaporated  to  apparent  dryness,  the  dish 
is  removed  and  placed  for  half  an  hour  in  the  hot-air  oven,  in 

60 


THE    SOLID    RESIDUE  6t 

order  that  the  "  solid  residue  "  may  be  finally  dried  at  105'^  C. ; 
the  object  being  to  remove  all  adventitious  moisture,  but  not 
the  water  which  is  an  essential  constituent  of  the  substance  as 
"  water  of  crystallization." 

3.  The  dish  is  removed  from  the  oven,  and  then  allowed  to 
cool  under  a  desiccator. 

4.  In  fifteen  minutes  the  dish  and  its  contents  are  weighed, 
and  the  difference  between  the  weight  found  and  that  of  the 
clean  and  empty  dish  represents  "  the  total  solids  "  in  50  c.c. 
of  water. 

5.  By  means  of  a  pair  of  platinum-pointed  crucible-tongs  the 
dish  is  next  held  in  the  flame  of  the  Bunsen  burner  and  slowly 
heated  to  dull  redness,  when  any  organic  matter  will  give  evidence 
of  its  presence  by  charring.  If  in  small  amount,  this  charring 
only  causes  an  evanescent  brown  shade  of  coloration  to  spread 
over  the  residue;  but  if  large  quantities  are  present,  the  organic 
matter  during  incineration  shows  blackened  specks  or  patches, 
which  slowly  disappear  and  give  off  dark  fumes  which  may 
possess  an  odour  of  burnt  hair  or  horn  when  due  to  nitrogenous 
animal  matter,  or  of  burning  sugar  if  the  material  is  vegetable. 
When  a  large  amount  of  oxidized  compounds  of  nitrogen  exist, 
they  may  give  rise  to  an  evolution  of  red  fumes  of  nitrogen 
dioxide.  Marked  scintillation  is  sometimes  also  perceptible — 
that  is  to  say,  tiny  sparks  are  emitted.  Eventually  nothing 
remains  but  clear  white  or  grey  mineral  ash,  except  where  iron  is 
markedly  present  and  imparts  a  reddish  tint  to  the  ash. 

6.  The  dish  is  allowed  once  more  to  cool  under  the  desiccator 
and  is  reweighed;  then  the  excess  of  weight  over  that  of  the 
clean  and  empty  dish  consists  solely  of  mineral  ash,  and  repre- 
sents the  "  non- volatile  solids." 

7.  The  weight  of  the  total  solids;  less  the  weight  of  the  "  non- 
volatile solids  "  represents  the  "  volatile  solids." 

Example. — ^The  clean  platinum  dish  weighs  44-225  grammes. 

The  dish  +  the  total  solids  weighs  44-245  grammes. 

.-.  44-245  -44-225  =  0-020  gramme  of  total  solids  in  50  c.c.  of 
water,  or  0-040  gramme  in  100  c.c.  (100  grammes). 

.-.  there  is  0-040  gramme  of  total  solids  in  100  grammes  of  water 

Or  40  parts  per  100,000  of  total  solids. 

After  ignition  the  dish -j- contents  weigh  44-240  grammes. 

.-.  the  "  non- volatile  soHds  "  in  50  c.c.  water  =44-240  -44-225 
=  0-015  gramme. 


62  LABORATORY   WORK 

.-.  there  is  0-030  gramme  in  100  grammes  of  water. 
Or  30  parts  -per  100,000  of  "  non-volatile  solids." 
Titus  the  total  solids  amount  to  40  parts  and  the  non-volatile 
solids  to  30,   and  the  difference  of  10  parts  per  100,000  will 
represent  the  volatile  solids. 

Notes. — It  may  be  pointed  out  that  a  few  drops  of  dilute  hydro- 
chloric acid  will,  by  creating  little  or  much  effervescence,  roughly 
indicate  the  amount  of  carbonates  present,  and  will  generally 
dissolve  out  everything  but  silica  and  the  sulphates  of  calcium 
and  magnesium. 

In  the  case  of  mineral  medicinal  waters  and  those  used  for 
some  trade  purposes,  a  detailed  and  complete  analysis  of  the 
mineral  ash  ma}'  be  required;  but  for  public  health  purposes,  in 
view  of  the  information  which  is  acquired  in  other  steps  of  the 
analysis,  a  complete  anatysis  of  the  ash  is  not  necessary.  This 
matter  is  therefore  beyond  the  scope  of  this  work ;  but  it  may  be 
stated  that  in  regard  to  the  principles  which  guide  chemists  as 
to  the  association  of  the  different  acids  and  bases  to  form  the 
saline  matter  in  w^ater,  it  is  assumed  that  the  combinations  are 
governed  by  their  respective  affinities — that  is  to  say,  the 
strongest  acid  is  assumed  to  be  combined  with  the  strongest 
base,  due  attention  being  also  paid  to  the  greater  or  less  degree 
of  solubility  of  the  salts,  since  it  is  well  known  that  this 
exercises  a  considerable  influence  on  the  manifestations  of  the 
force  of  affinity. 

Thus  it  is  assumed  that  the  chlorine  is  combined  with  sodium; 
any  excess  being  allotted  to  potassium,  or,  in  the  absence  of 
potassium,  to  calcium.  If  there  is  excess  of  sodium,  it  and  the 
potassium  are  assumed  to  be  in  combination  with  sulphuric  acid, 
any  excess  of  which  is  allotted  to  calcium  and  magnesium;  and 
calcium  and  magnesium,  if  not  combined  with  sulphuric  acid, 
nitric  acid,  or  chlorine,  are  in  the  form  of  bicarbonates. 

Nitric  acid  is  held  to  be  combined  with  ammonia,  and  when 
there  is  excess  it  is  allotted  to  either  soda  or  lime  or  magnesia 
(as  circumstances  indicate)  in  waters  which  are  found  to  be  com- 
paratively free  from  organic  matter;  otherwise  it  may  be  allotted 
to  fixed  organic  bases. 

The  other  constituents  of  the  mineral  residue,  being  in  such 
small  amounts,  are  generally  not  grouped  as  salts ;  the  silica,  iron, 
alumina,  nitrous  acid,  and  phosphoric  acid  being  returned  as 
SiOg,  FegOg,  AI2O3,  N2O3,  and  P2O5,  respective!}-. 


THE    SOLID    RESIDUE 


63 


To  give  a  simple  example: 

A  mineral  water  is  analyzed  and  found  to  contain: 


Sulphuric  acid 
Soda  . . 
Magnesia 
Chlorine 
Lime  . . 
Carbonic  acid 


Parts  per  100,000. 

186-07 

6672 

5276 

13-40 

6-68 

2-12 


32775 


These   constituents   would  be   expressed   in   combination   as 
follows : 


Sulphate  of  magnesium 

158-28 

Sulphate  of  sodium  . . 

132-86 

Sulphate  of  calcium 

9-69 

Chloride  of  sodium  . . 

22-11 

Carbonate  of  calcium 

4-81 

32775 

The  ignited  residue  may  be  retained,  as  a  routine  practice,  for 
the  estimation  of  phosphoric  acid.  A  loose  white  light  residue 
indicates  the  presence  of  magnesium. 

Most  good  waters  furnish  a  sohd  residue,  which,  when  ignited, 
shows  no  darkening ;  but  the  sohds  of  potable  peaty  waters  may 
show  marked  charring. 

Surface  waters  generally  furnish  from  5  to  20  parts  of  total 
solids,  according  to  the  nature  of  the  surface ;  well  waters  from 
20  to  60,  or  over. 

The  total  solids  have  been  estimated  even  above  300  parts 
per  100,000  in  certain  deep-well  waters. 

A  high  amount  of  mineral  solids,  consisting  as  it  so  frequently 
does  of  harmless  salts  (such  as  calcium  carbonate),  is  not  neces- 
sarily injurious;  but  if  a  goodly  proportion  of  the  mineral 
residue  is  found  to  be  contributed  by  sulphates,  the  water  ma}- 
be  productive  of  digestive  disturbances;  and,  generally  speaking, 
the  mineral  matter  in  a  domestic  water-supply  should  not  exceed 
100  parts  per  100,000.  *  • 


CHAPTER  VIII 


THE  EXAMINATION  OF  SUSPENDED  AND  DEPOSITED 
MATTER  IN  WATER 

Chemical. — The    estimation    and    examination    of    the    "  total 
solids  "    have   only   included   those   solids   which   are   in    solu- 
tion, but  some  samples  of  water  contain  suspended  matter  and 
sediment. 

The  most  simple  method  by  which  the  matter 
which  will  deposit  can  be  collected  and  esti- 
mated is  the  following:  After  well  shaking, 
remove  a  litre  of  the  sample;  place  it  in  a  large 
conical  flask;  cover  up  and  set  aside  for  twenty- 
four  hours;  decant  or  syphon  off  as  much  of  the 
supernatant  water  as  it  is  safe  to  do  without 
running  any  risk  of  disturbing  the  deposited 
matter;  the  deposit  should  then  be  shaken  up 
with  about  200  c.c.  of  distilled  water,  and  after 
deposition  that  remaining  behind  in  the  flask 
should  then  be  washed  by  distilled  water  into  a 
platinum  dish,  dried,  and  weighed. 

The  sediment  may  then  be  carefully  in- 
cinerated at  as  low  a  temperature  as  possible, 
and  the  volatile  and  non-volatile  matter  esti- 
mated. 

Wynter  Blyth's  tube  is  a  convenient  instru- 
ment for  collecting  water  sediments;  as  seen  in 
Fig.  10,  it  is  similar  in  appearance  to  a  large 
pipette  capable  of  holding  a  litre  of  water,  A 
small  glass  cell  fits  over  the  small  lower  ex- 
tremity of  the  tube,  and  into  this  the  deposited  matter  gradually 
collects.  After  the  insertion  of  the  long  rod-shaped  stopper, 
which  plugs  the  outlet  to  the  tube,  the  cell  can  easily  be  removed 

64 


fig.  10. wynter 

blyth's  tube 
for  collecting 
sediments. 


SUSPENDED    AND    DEPOSITED    MATTER 


65 


without  the  sediment  being  disturbed.  This  may  then  be  trans- 
ferred to  a  platinum  dish,  dried  and  weighed. 

Recently  washed  and  ignited  fine  quartz  sand  may  be  cm- 
ployed  to  filter  off  the  material  for  microscopic  examination; 
all  the  filtered  material  from  a  large  bulk  of  water  thus  collected 
may  be  subsequently  washed  out  by  a  little  distilled  water  and 
examined. 

Where  a  sediment  forms  from  a  sample  of  water  advantage 
should  be  taken  of  the  valuable  evidence  as  to  its  nature  which 


FIG.   II. SHOWING  THE  SEDIMENT  OF    A  POND-WATER,  A  SAMPLE  OF  WHICH 

WAS    COLLECTED    IN    THE    EARLY    SPRING    (X    250).        DRAWN    BY    A.    E. 
EVANS,  M.B. 

I,  A  desmid;  2,  Tabellaria  floccosa  (Diatomaceae) ;  3,  actinophrys ;  4,  a 
confervoid  growth;  5,  a  vegetable  spiral  vessel;  6,  silicious  particles; 
7,  conferva;  8,  gomphonema.  Various  forms  of  minute  unicellular 
plants  are  seen  scattered  about  the  "  field." 

a. microscopic  examination  affords.  Some  of  the  sediment  maj^ 
be  taken  up  by  means  of  a  small  pipette,  and  transferred  to  several 
glass  slides  and  cover-glasses  applied,  any  excess  of  water  upon 
the  shde  being  removed  by  clean  blotting-paper;  or,  better  still, 
the  sediment  may  be  collected  by  means  of  centrifugalization, 
and  the  deposit  from  the  centrifuge  may  be  mounted  and 
examined.  When  suspended  matter  is  so  light  that  it  will 
not  settle,  drops  of  the  water  must  be  examined  under  the 
microscope. 

If  a  quantitative  estimation  is  desired,  the  water  should  be 

5 


66  LABORATORY   WORK 

allowed  to  rest  for  twenty-four  hours,  so  as  to  exclude  matter 
which  will  deposit,  and  the  total  solids  in  the  supernatant  water 
are  then  estimated;  the  solids  remaining  should  be  ascertained 
after  the  same  water  has  been  filtered  through  a  Pasteur  filter; 
and  the  difference  in  the  two  estimations  will  represent  the 
amount  of  suspended  matter  retained  by  the  filter. 

The  various  forms  of  animal  and  vegetable  life  (exclusive  of 
bacteria),  and  of  inanimate  organic  and  inorganic  matter,  are 
best  sought  after  by  commencing  with  the  ^-inch  power,  and 
next  passing  on  to  the  :^-inch  power. 

The  presence  of  living  organisms  in  abundance,  bearing  as  they 
generally  do  a  ratio  to  their  food-supply,  will  be  often  sufficient 
in  itself  to  condemn  the  water  as  containing  a  considerable 
amount  of  organic  (mainly  vegetable)  pollution.  The  fact  that 
animal  and  vegetable  life  have  powers  of  purifying  the  water  is 
beside  the  question;  their  very  presence  denotes  impurity,  and 
with  the  attainment  of  purit}?  they  mostly  disappear. 

The  higher  and  macroscopical  types  of  animal  life,  such  as 
water-fleas  and  other  Crustacea,  broadly  speaking,  denote  less 
danger  than  the  lower  and' more  minute  forms  (bacteria,  amoebae, 
infusoria).  The  former  are  generally  associated  with  suspended 
matter  in  waters  that  are  not  likely  to  be  used  for  drinking 
purposes  on  account  of  their  contamination  being  obvious  to 
the  senses,  while  the  latter  are  often  found  to  be  associated  with 
dissolved  organic  matter  in  waters  which  may  possess  excellent 
physical  characters. 

More  especially  do  large  numbers  of  bacteria  and  the  presence 
of  fungi,  infusorians,  and  anguillulse,  suggest  harmful  pollution. 
But  the  most  suspicious  elements  which  may  be  detected  by  a 
microscopical  examination  of  suspended  or  deposited  matter  are 
those  which  point  directly  to  sewage  contamination,  and  those 
which  point  indirectly  to  human  contamination.  The  latter  will 
be  found  in  hair,  wool,  cotton  and  linen  fibres,  epithelial  scales, 
etc.  The  former  include  objects  which  can  rarely  gain  access 
to  water  save  in  actual  sewage,  such  as:  (i)  Substances  which 
from  their  indigestibihty  commonly  leave  the  body  in  the  faeces; 
(2)  substances  which  ma}^  do  so  when  digestion  is  interfered  with ; 
and  (3)  eggs,  etc.,  of  animal  parasites  which  infest  the  human 
gastro-intestinal  tract.  Under  the  first  heading  would  be  em- 
braced such  substances  as — Various  connective-tissue  elements, 
fat  globules  and  crystals,  muscle  fibres,  starch  cells,  etc.     Under 


SUSPENDED    AND    DEPOSITED    MATTER 


67 


the  second  heading,  shreds  of  mucous  membrane,  epithehal  cells, 
gall-stones,  particles  of  various  kinds  of  foods  in  a  semi- digested 
state,  etc.  The  third  heading  would  include  T.  solium,  T.  medio- 
canellata,  Bothriocephalus  laius  (either  as  eggs  or  segments), 
Ascaris  lumbricoides,  Oxyuris  vermicularis,  Tricocephalus  dispar 
(ova  or  mature  forms),  Paramoecium  colt.  It  must  not  be  thought 
that  this  direct  evidence  of  human  contamination  is  obtainable 
except  on  rare  occasions. 


Matter  which  may  be  found  by  a  Microscopical 
Examination  of  Water. 

1.  Inanimate. 

(a)  Mineral. — ^This  may  be  examined  by  the  ^-inch  power,  and 
then  chemical  tests  applied  under  the  cover-glasses. 

Sand  and  flint  particles  generally  have  a  sharp  and  angular 


c   V 


FIG.    12. — VEGETABLE   TISSUE. 


A,  Vegetable  parenchyma  ;  B,  a  pitted  vessel  ;  C,  a  scaliform  vessel ; 
D,  a  spiral  vessel. 

outline,  though  often  somewhat  rounded  from  rolling  and  attri- 
tion ;  a  drop  of  hydrochloric  acid  let  to  run  under  the  cover-glass 
has  no  effect  upon  them. 

In  clay  and  marl  (silicate  of  alumina)  the  particles  are  amor- 
phous and  very  minute,  and  unaffected  by  hydrochloric  acid. 

Chalk  particles  are  likewise  amorphous,  mostly  somewhat 
larger  than  those  of  clay  and  marl,  and  generally  rounded  in 
outline.  A  drop  of  hydrochloric  acid  causes  them  to  disappear 
with  effervescence. 

Iron  peroxide  forms  a  yellowish-brown  amorphous  debris, 
soluble  (Hke  the  chalk^particles)  in  hydrochloric  acid,  and  blued 


68  LABORATORY  WORK 

when  a  drop  of  HCl  and  of  a  solution  of  ferrocyanide  of  potassium 
are  allowed  to  run  under  the  cover-glass. 

Mica  forms  thin,  fine,  scale-like  films  of  very  irregular  outline, 
and  insoluble  in  hydrochloric  acid. 

{b)  Vegetable. — Parenchyma;  the  dotted  ducts  and  spiral 
vessels  or  spiral  fibres;  pieces  of  the  cuticle  with  the  vegetable 
"  hairs  "  still  adhering;  pollen. 

Woody  fibres;  fragments  of  leaves,  etc. ;  starch  cells;  macerated 
paper;  linen  and  cotton  fibres;  dark  particles  of  soot. 

Vegetable  matter  often  appears  as  dark  flattened  structureless 
particles,  or  frequently  only  as  debris,  when  the  classification  of 
the  deposit  is  attended  with  great  difficulty;  if,  however,  any 
spiral  vessels,  or  fibres,  or  dotted  ducts  can  be  distinguished, 
these  will  always  point  to  the  probable  nature  of  any  obscure 
debris,  etc.,  with  which  they  are  associated. 

(c)  Animal. — Hairs;  feathers;  down;  wool  or  silk  fibres. 
Striped  muscular  fibres;  fat  globules  and  crystals;  connective 
tissue ;  epithelial  scales ;  shreds  of  mucous  membrane. 
Scales  and  wings,  legs,  etc.,  of  insects. 

Reddish-brown  globular  masses  are  sometimes  found  in  asso- 
ciation with  grosser  sewage  pollution.  Their  nature  is  somewhat 
obscure. 

The  following  particulars  will  serve  for  the  microscopic  identi- 
fication of  textile  fibres  {vide  Plate  I.). 

Linen. — Cylindrical  jointed  fibres,  with  minute  branching 
filaments  at  intervals. 

Cotton. — Flattened  t\visted  fibres,  with  no  joints  or  nodes  and 
no  branching  filaments  or  transverse  markings.  The  apex  of 
the  fibre  is  blunt. 

Wool. — Rounded  fibres,  with  fine  cross-markings  and  indenta- 
tions on  the  border  at  the  site  of  the  cross-markings.  A  central 
longitudinal  canal  exists,  but  this  is  generally  obliterated.  The 
fibres  stain  yellow  with  a  saturated  aqueous  solution  of  picric 
acid,  warmed  and  then  allowed  to  cool — not  so  those  of  linen. 

Silk. — Long  cylindrical  fibres  with  a  well-defined  central 
canal,  but  no  cross-markings  or  indentations.  The  fibres  dis- 
solve rapidly  in  concentrated  H2SO4 — not  so  those  of  wool. 

Hemp. — Fibres  faintly  striated,  with  central  canal,  and  trans- 
verse and  oblique  lines  cross  the  fibres.  (These  are  rendered 
more  distinct  by  chloral  hydrate.)  A  transverse  section  of  fibres 
is  irregular!}'  rounded.     The  ends  of  the  fibres  are  usually  blunt. 


SUSPENDED    AND    DEPOSITED    MATTER  69 

Flax. — Closely  similar  to  hemp,  but  the  ends  of  the  fibres 
taper  to  fine  points.  The  fibres  are  polygonal  in  transverse 
section. 

2.  Animate. 

Vegetable. —Winnie  forms  of  vegetable  life  mostly  belong  to 
the  class  of  cryptogamous  {i.e.,  non-flowering)  plants,  and  con- 
tain chlorophyll.     They  may  be  divided  into — 

I.  Small  and  microscopic  fungi,  which  represent  some  of  the 
lowest  forms  of  vegetable  growths.  These  may  be  present  as 
spores,  sporangia,  or  my  cell  a. 

Both  Bacterium  termo  and  Sarcina  ventriculi  present  familiar 
instances  of  these  forms. 

Beggiatoa  alba  has  been  badly  named  "  the  sewage  fungus," 
but  any  water  containing  a  high  amount  of  sulphuretted  hydrogen 
or  sulphate  is  capable  of  supporting  this  fungus,  quite  indepen- 
dently of  the  source  from  which  such  sulphur  compounds  are 
derived,  and  certain  other  growths  are  found  even  more  frequently 
in  association  with  sewage  pollution.  In  Beggiatoa  alba  the 
sheathless  cylindrical  filaments  contain  roundish  particles  of 
sulphur,  which  are  highly  refractile  to  light. 

Leptothrix  presents  under  the  microscope  a  similar  appearance 
to  that  of  Beggiatoa  alba,  but  the  cylindrical  cells,  connected  in 
threads  and  surrounded  by  a  sheath,  exhibit  no  sulphur  granules. 
The  empty  sheaths  may  form  large  brownish  deposits  in  water 
containing  iron.  Leptomitiis  lacteus  forms  soft  white  or  dirty 
tufts  attached  to  stones  or  channels.  In  the  absence  of  oxygen 
the  growth  darkens  and  putrefies.  Under  the  microscope  long 
branching  filaments,  constricted  at  regular  intervals  and  bearing 
zoospores  on  the  terminal  segments,  are  seen.  Sphcerotilus  nutans 
is  a  similar  growth,  presenting  under  the  microscope  chains  of 
long  undivided  filaments.  Cladothrix  may  be  found  to  be  abun- 
dant in  iron  waters;  the  threads  are  composed  of  rod-shaped  cells 
surrounded  by  a  thin  sheaf. 

An  aquatic  plant  known  as  crenothrix  gives  much  trouble  at 
times,  because  of  its  tendency  to  develop  in  the  water-mains  and 
to  clog  water-pipes.  Under  the  microscope  this  plant  presents 
cylindrical  filaments  transversely  divided  into  cells,  and  these 
filaments  are  surrounded  by  a  gelatinous  sheath  which  is  coloured 
by  a  deposit  of  ferric  oxide.  The  cells  may,  by  division  and 
production  of   viscous   matter,    escape   and   form   zooglota.     A 


70  LABORATORY   WORK 

drop  of  dilute  hydrochloric  acid  let  under  the  cover-slip  dissolves 
up  the  iron,  and  enables  the  plant  structure  to  be  more  clearly 
defined.  Iron  is  requisite  for  its  growth,  and  it  is  absent  from 
waters  which  are  but  slightly  ferruginous.  It  is  often  discovered 
in  mains  quite  unexpectedly,  and  its  long  rusty  filaments  have 
been  sometimes  taken  for  horse-manure,  with  a  consequent  poor 
opinion  of  the  character  of  the  water-supply.  Removal  of  the 
iron  by  oxidation  and  filtration  is  the  best  guarantee  against  the 
occurrence  of  this  growth. 

Mucor,  Aspergillus,  and  PeniciUium  are  moulds  which  may 
often  be  found  in  stagnant  water.  These  are  illustrated  on 
pp.  263,  264,  and  280. 

2.  Nitmeroiis  forms  of  algcB,  ranging  in  size  from  those  visible 
only  at  high  microscopic  powers  to  those  visible  with  the  naked 
ej^e.  Of  these  there  are  man}^  families:  The  volvocineae,  of 
which  volvox  is  the  type,  include  the  lowest  vegetable  forms 
of  minute  organisms;  the  oscillatoria  exhibit  a  pendulum-like 
motion;  the  confervaceas  are  ver}^  numerous. 

Volvox  glohator  forms  a  green  colony  of  cells.  The  colony  is 
spherical,  and  the  individual  cells  live  in  the  wall  of  the  sphere, 
each  having  two  flagella  and  a  nucleus.  The  ball,  or  hollow 
colom%  continually  rotates  by  means  of  the  flagella  of  each 
indi\idual.  This  organism  gives  rise  to  a  fishy  taste  and  odour 
in  water. 

Protococcus  phwialis  is  an  interesting  instance  of  an  algoid 
plant  which  can  live  in  the  atmosphere,  and  which  may  be  found 
in  rain-water.     Raphidium  and  Scene desmus  are  not  uncommon. 

Clathrocystis  and  Microcystis  are  widely  distributed  in  surface 
waters. 

Of  diatoms,  Asterionella  and  Navicula  are  familiar  types. 

The  algae,  when  in  considerable  quantities,  may  furnish  a 
dark  green,  repulsive  appearance  to  the  water,  and  may  give 
rise  to  diarrhoea;  when  they  die  and  decay  the  water  acquires  an 
offensive  taste  and  odour. 

In  winter  comparatively  few  of  such  growths  are  found.  In 
spring  various  diat-oms  appear;  these  will  disappear  in  a  few 
weeks,  and  in  their  place  will  come  the  green  algae;  in  the  fall 
these  will  disappear,  and  the  diatoms  develop  again — in  turn  to 
disappear  with  the  onset  of  winter  (Whipple).  They  {tahellaria, 
asterionella,  etc.)  occasionally  grow  in  large  numbers  on  the  surface 
of  stagnant  water,  or  even  on  filter-beds. 


SUSPENDED    AND    DEPOSITED    MATTER  7I 

Animal. — i.  Protozoa,  (a)  Rhizopoda.  .4 m«&a  will  be  recog- 
nized by  its  characteristic  amoeboid  movement.  AmrehcB  coli 
are  found  in  the  mucus  of  the  discharges  of  persons  suffering 
from  dysentery.  Actinophrys,  the  body  of  which  is  surrounded 
by  stiff  radiating  pseudopodia,  is  another  common  and  famiUar 
form;  and  polyps  shows  a  very  low  type  of  structure.  In 
Spongilla  fluviatilis  (the  fresh- water  sponge)  the  animal  substance 
is  spread  over  a  network  of  spicules;  it  grows  in  green  masses. 

Difflugia  has  a  coating  formed  by  sand  which  it  has  taken  into 
its  body,  and  with  which  it  makes  a  globular  shell  inside  of  which 
is  the  soft  protoplasm  of  the  body  substance;  this  flows  out  at 
the  mouth  of  the  shell  and  forms  anastomosing  threads,  which, 
acting  as  a  net,  catch  food.      Cercomonas  and  Euglena  viridis 

are  also  common.     Euglena  is  actively  motile  and  green  from 

chlorophyll. 

{b)  Infusoria.     Paramcecium,    vorticella,    and    coleps    are    all 

common  types. 

Stentor  is  among  the  largest  of  this  class,  and  is  so  named 

from  the  trumpet-Hke  shape  of  the  body.     It  is  covered  with 

small  ciha,  and  possesses  long  cilia  in  front. 

Coleps  is  also  covered  with  ciha,  and  has  an  opening  surrounded 

by  short  spines  at  both  ends. 

Paramcecium  is  flattened  and  covered  with  ciha.     Paramcecium 

coli    are    sometimes    associated    with    diarrhoeal    discharges    in 

human  beings,  and  Cercomonas  intestinalis  (a  protozoan)  may  be 

present  in  the  mucous  discharges  of  children.     Paranema  is  one 

of  the  simplest  of  the  infusoria;   it  possesses  one  flagellum. 

Vorticella  possesses  a  long  contractile  stalk.     The  body  has  a 

lid,   and  both  the    hd    and    the    opening  into  the  gullet  are 

ciliated. 

2.  Ccelenterata. — Hydra  is  a  common  type  of  this  sub-kingdom. 

3.  Annulosa.^ — This  sub-kingdom  embraces — 

{a)  Crustacea,  including  the  amphipoda,*  isopoda,t  and 
branchiopoda.  % 

*  The  amphipoda  are  sessile-eyed  malacostracans.  Their  bodies  are 
compressed  laterally,  the  eyes  are  immobile,  and  the  feet  are  directed 
partly  forwards  and  partly  backwards. 

f  The  isopoda  possess  sessile  eyes  and  a  depressed  body,  and  the  feet 
are  of  equal  size  and  move  in  the  same  direction. 

X  The  branchiopoda  are  so  called  because  their  branchias  or  gills  are 
situated  on  the  feet.  The  head  is  not  distinct  from  the  thorax,  which  is 
much  reduced  in  size. 


72  LABORATORY  WORK 

Cyclops  qiiadricornis,  Gammarus  pulex,  and  Daphnia  pidex 
are  familiar  types  of  this  class.  In  the  latter  the  antennae 
act  ,as  oars  and  propel  the  little  animal  through  the  water  by 
a  series  of  short  springs  or  jerks;  the}^  assume  a  red  colour  in 
summer,  and  when  in  swarms  they  give  a  bloody  tinge  to  the 
water. 

(b)  Arachnida,  including  the  microscopic  tardigrada  or  "  water- 
bears." 

(c)  Insecta.     Either  in  the  larval,  pupal,  or  adult  forms. 

4.  Annuloida. — This  sub-kingdom  embraces  the  scolecida,  and 
includes  turbellaria,  rotifera  (or  wheel-animalcules),  tseniadea, 
naematoidea,  anguillulse  (water- worms). 

Rotifer  vulgaris. — Gives  a  red  or  green  colour  to  gutter-water. 
It  is  often  called  the  "  wheel  "  animalcule  on  account  of  its 
circular,  oval  disc,  which  is  fringed  with  ciha;  it  is  motile,  and  by 
its  movements  conveys  an  appearance  of  rotation;  the  cilia  serve 
to  propel  the  animal  and  to  set  up  food  currents. 

Small  water-leeches  {HirudinidcB)  found  in  fresh  water  and  on 
wet  grass  may  be  distinguished  by  their  two  suckers,  one  at  either 
extremity;  the  mouth,  armed  with  three  teeth,  is  set  in  the  middle 
of  the  anterior  sucker. 

5.  Mollusca. — Including  polyzoa,  siphonida,  etc. 

The  various  human  parasites  which  may  be  conveyed  through 
the  medium  of  water  are — 

The  segments  and  eggs  of  tape- worms  {Tcenia  solium,  T.  medio- 
canellata,  T.  echinococcus,  and  Bothriocephalus  latiis) ;  the  Guinea- 
worm  {Dracunciilus  medinensis);  the  round- worm  [Ascaris  lum- 
hricoides);  the  threadworm  [Oxyuris  vermicularis);  Bilharzia 
hamatobia  ;  Ankylostomwn  duodenale  ;  Tricocephahis  dispar  (the 
whip-worm);  Filaria  sanguinis  hominis  ;  the  filarial  stage  of 
Distoma  hepaticimi  (the  liver-fluke  of  sheep). 

Several  of  these  may  be  found  in  either  embr^'onic  or  adult 
stages  of  development. 

The  ova  of  bothriocephalus  are  developed  in  fishes,  and  man  can 
only  be  infected  by  eating  the  latter.  The  larva  of  Ankylostomum 
duodenale  is  developed  from  ova  in  foul  waters,  and  man  may 
become  infected  by  handling  and  drinking  such  water.  The 
smooth  oval  egg  of  Ankylostomum  duodenale  possesses  a  seg- 
mented yoke  when  it  leaves  the  female.  After  being  discharged 
in  faeces,  under  suitable  conditions  of  moisture  and  temperature 
an  embr3^o  forms,  which  after  a  few  days  passes  a  sluggish  exist- 


SUSPENDED    AND    DEPOSITED    MATTER  73 

ence  usually  in  damp  mud  or  earth.  It  may  thus  live  for  weeks 
or  months,  and  if  it  gains  access  to  the  small  intestine  of  the 
human  being  the  worm  reaches  sexual  maturity  in  about  a  month. 
The  adult  worm  is  a  small  nematode  with  a  mouth  furnished 
with  four  strong  projecting  hooks  and  two  conical  teeth,  and 
the  tail  of  the  male  has  a  large  umbrella-like  expanded  bursa 
from  which  two  long  thin  spicules  project. 

Man  is  very  rarely  infected  by  the  larvse  of  Distoma  hepatictim. 
The  ova  develop  in  water  into  cihated  embryos,  and  these 
undergo  in  small  water-snails  {Limnceus  truncatulus)  a  further 
development  to  larvae;  these  ultimately  change  into  little 
organisms  (cercaria)  resembhng  tadpoles,  which  either  remain 
encysted  in  water-snails  or  leave  them  and  become  attached 
by  their  suckers  to  grass. 

Bilharzia  hcematobia. — The  male  is  a  grey  flattened  trematode 
worm,    -|-   inch  in   length,   which  inhabits   the   portal,    splenic, 


FIG.    13. — -CILIATED    EMBRYO    AND    CERCARIA    FORM    OF 
DISTOMA    HEPATICUM    (MAGNIFIED). 

mesenteric  veins  and  the  inferior  vena  cava  of  man  and  of  some 
species  of  apes,  especially  in  Africa  and  India;  posteriorly  the 
sides  of  the  parasite  curve  towards  each  other  and  meet  to  form 
a  channel  (the  gynecophoric  canal),  in  which  part  of  the  long 
slender  female  (f  inch  in  length)  lies  during  fecundation.  The 
spindle-shaped  ova  possess  a  beak,  which  generally  projects 
from  one  end,  but  sometimes  laterally ;  these  ova  may  be  hatched 
before  the  parasite  leaves  the  tissues  of  the  original  host,  but  the 
embryos  are  not  born  until  afterwards.  If  the  ova  find  their 
way  into  water,  their  walls  swell  up  and  rupture  and  the  minute 
embryos  escape,  armed  with  cilia  which  serve  to  project  them 
through  the  water.  Apparently  the  embryo  becomes  attached 
to  some  fresh-water  mollusc  (or  possibly  fish),  and  develops  into 
a  cercaria  form.  Probably  man  is  not  infected  by  drinking 
water,  but  by  protracted  immersion  in  contaminated  water,  when 


74  LABORATORY    WORK 

the  parasite  enters  the  urethra  or  anus.  The  parasite  is  in- 
capable of  reproducing  itself  within  the  human  body. 

The  embrj^o  of  Filaria  medinensis,  or  the  Guinea-worm,  is  also 
aquatic  in  habit — indeed,  its  first  stages  of  development  occur  in 
a  fresh-water  crustacean.  From  these  facts  the  inference  that 
the  parasite  is  transferred  to  man  bj^  drinking  water  is  justifiable. 

Of  the  Filaria  sanguinis,  the  embryo  of  one  of  these  {Filaria 
nocturna)  has  been  traced  through  the  body  of  the  mosquito,  and 
so  into  water,  by  which  it  may  enter  the  human  body — although 
it  is  usually  inoculated  directly  by  the  bite  of  the  insect. 

Tricocephalus  dispar  is  also  transmitted  by  water,  for  the  egg 
develops  only  in  water  or  upon  some  very  damp  medium,  and 
the  liberated  embryo  may  thus  find  its  way  and  attach  itself  to 
the  mucous  membrane  of  the  caecum. 

There  are  other  human  parasites  which  infect  their  host  fre- 
quently through  the  medium  of  drinking-water,  although  their 
life-histories  do  not  even  include  a  temporary  residence  in  water. 
Thus  the  ova  of  Ascaris  Imnhricoides  and  of  TcBiiia  echinococcus 
are  often  washed  into  water  or  blown  into  it  as  dust.  The  ova 
of  the  female  ascaris  are  discharged  with  the  faeces  of  the  host, 
when,  but  not  before,  they  are  capable  of  furnishing  embryos; 
these  probably  have  an  independent  existence  (possibly  in  water 
or  some  intermediate  host,  such  as  worms  or  insects)  before  again 
entering  the  human  body  and  completing  their  development. 

It  may  be  stated  that,  as  a  general  rule,  with  one  or  two  excep- 
tions— such  as  Oxyuris  vermicularis,  Trichina  spiralis,  and  the 
tape-worms — contaminated  water  is  the  principal  means  by 
which  the  entozoa  of  man  pass  into  his  system.  The  ova  of 
0.  vermicularis,  unlike  those  of  A.  lumhricoides,  contain  embryos 
prior  to  their  discharge,  but  probably  these  are  incapable  of 
further  development  until  they  have  been  passed  with  the  faeces, 
when  they  may  reinfect  the  same  individual  or  others  occupying 
the  same  bed,  etc. ;  or  may  pass  into  water,  or  get  deposited  upon 
vegetables  and  fruit  and  thus  get  ingested. 

The  animal  parasites  of  the  lower  animals  also  supply  many 
instances  of  transmission  by  water. 


CHAPTER  IX 

ORGANIC  MATTER  IN  WATER 

Organic  pollution  may  be  of  animal  and  vegetable  matter;  and 
since  the  danger  of  these  two  forms  of  organic  contamination 
differs  very  materially  (animal  matter  being  far  more  dangerous 
than  vegetable),  it  is  important  to  learn  the  nature  as  well  as 
the  amount  of  any  organic  matter  which  is  fouling  water. 

Organic  matter,  as  is  well  known,  becomes,  under  suitable 
conditions  of  temperature,  air,  and  moisture,  resolved  into 
simpler  parts,  by  fermentation,  putrefaction,  and  slow  oxidation. 
As  the  ultimate  result  of  these  processes,  the  carbon  appears 
as  carbonic  acid,  the  hydrogen  as  water,  and  the  nitrogen  as 
ammonia,  nitric  and  nitrous  acids.  When  putrefaction  sets  in, 
odorous  gases  are  evolved,  which  mostly  consist  of  compounds 
of  sulphur. 

The  effort  to  estimate  the  organic  matter  from  the  amount  of 
oxygen  of  which  it  will  deprive  the  permanganate  of  potassium 
was  practised  almost  universally  for  a  long  period,  and  it  remains 
as  an  auxiliary  test  for  organic  matter  to  this  day.  The  facts 
that  potassium  permanganate  in  solution  is  so  very  unstable, 
that  other  substances  in  the  water — apart  from  organic  matter — 
are  capable  of  reducing  it,  that  it  will  part  with  its  oxygen 
readily  to  the  less  dangerous  {i.e.,  vegetable)  as  well  as  to  the 
more  dangerous  {i.e.,  animal)  pollution,  and  that  the  oxidizable 
organic  matter  bears  an  unknown  and  inconstant  ratio  to  the 
total  organic  matter,  all  conduced  to  some  dissatisfaction  with  the 
test,  and  endeavours  have  been  made  to  find  others  which  are  of 
greater  service. 

E.  Frankland  devised  a  most  ingenious  process  to  meet  the 
want,  but  it  is  quite  unsuited  to  the  bulk  of  health  officers,  and 
there  is  scope  for  some  error  of  experiment  to  creep  in  even  with 
practised  hands.     In  this  process  a  measured  volume  of  water 

75 


76  LABORATORY   WORK 

is  evaporated  to  a  solid  residue,  and  this  is  collected  in  a  hard 
glass  combustion  tube,  mixed  with  oxide  of  copper,  and  burnt 
in  a.  furnace.  The  oxide  of  copper  parts  with  its  oxygen  to  the 
organic  matter,  which  is  completely  destro^^ed,  and  the  carbonic 
acid,  nitric  oxide,  and  nitrogen  which  result  are  collected, 
measured,  and  expressed  in  terms  of  "  organic  carbon  "  and 
"  organic  nitrogen." 

A  method  superior  in  the  facility  of  its  execution,  and  equally 
as  valuable  for  the  purpose  at  issue,  is  that  known  as  "  the 
Wanklyn,  Chapman  and  Hall  Process."  By  it  an  endeavour  is 
made,  after  computing  the  amount  of  "  free  and  saline  "  ammonia 
originaUy  present  in  the  water,  to  estimate  the  amount  of  nitro- 
genous organic  matter  present  from  the  amount  of  ammonia 
which  can  be  derived  from  the  breaking  up  of  such  matter  by 
strongly  alkaline  permanganate  of  potassium  at  the  boiling 
temperature.  The  organic  matter  which  gains  access  to  water 
is  largely  nitrogenous,  and  a  very  delicate  indication  of  its 
presence  and  amount  may  be  obtained  from  the  nitrogen  which 
it  furnishes. 

Great  importance  is  also  attached  in  this  process  to  the  amount 
of  the  "  free  and  saline  "  ammonia  originally  in  the  water,  for  it 
is,  generally  speaking,  a  product  of  recent  animal  contamina- 
tion. It  will  be  recalled  that  one  of  the  chief  nitrogenous  sub- 
stances in  sewage  is  urea;  and  this  urea,  by  the  action  of  the 
Micrococcus  urecR,  is  rapidly  converted  into  saline  ammonia, 
thus: 

CO(NH2)2  +  2H20=  (NHJ^COg. 

It  is  obvious  that  no  chemical  process  can  determine  as  to 
whether  the  organic  matter  is  Hving  or  dead,  or  whether  in  the 
former  case  it  is  harmful  or  not ;  but  while  considerable  quantities 
of  the  germs  of  disease  cannot  by  themselves  appreciably  affect 
the  amount  of  "  albuminoid  ammonia,"  since  they  always  gain 
access  to  water  along  with  other  organic  matter,  this  latter 
often  furnishes  by  chemical  analysis  the  evidence  of  danger. 


CHAPTER  X 
WANKLYN'S  PROCESS 

Special  Reagents  required : 

1.  A  standard  solution  of  chloride  of  ammonium,  made  to  the  strength 
that  I  c.c.  contains  o-oi  milligramme  of  ammonia. 

The  solution  is  made  by  dissolving  3-14  grammes  of  pure  chloride  of 
ammonium  in  a  litre  of  distilled  ammonia-free  water;  if  some  of  this  is 
diluted  a  hundredfold  with  distilled  ammonia-free  water,  it  is  of  the 
required  strength. 

2.  Nessler's  reagent.  This  consists  of  a  saturated  solution  of  the  per- 
iodide  of  mercury  in  distilled  ammonia-free  water,  the  whole  being  rendered 
strongly  alkaline  with  caustic  potash.  When  this  reagent  is  applied  to  a 
solution  containing  ammonia,  it  imparts  a  colour  varying  from  a  faint 
yellow  to  a  reddish-brown,  or  even  a  precipitate,  according  to  the  amount 
of  ammonia  present.  This  reaction,  which  is  due  to  the  formation  of 
ammonio-mercuric  iodide 

(2(2KI,Hgl2)4-NH3-|- 3KHO=NHg2lH20-^  7KI-I- 2H2O). 

is  not  shared  by  organic  matter  as  such. 

The  solution  of  the  reagent  should  have  an  extremely  faint  yellow  colour, 
which  indicates  that  it  is  saturated  with  the  periodide  of  mercury,  and  is 
therefore  "  sensitive  ";  should  it  be  colourless  and  non-sensitive,  this  can 
be  corrected  by  the  addition  of  a  drop  or  two  of  a  saturated  solution  of 
corrosive  sublimate. 

Any  precipitate  of  mercuric  iodide  which  settles  should  not  be  disturbed 
when  the  reagent  is  being  used. 

The  following  has  been  found  the  best  method  of  preparing  Nessler's 
reagent:  Dissolve  13  grammes  of  corrosive  sublimate  in  about  250  c.c.  of 
water,  and  35  grammes  of  iodide  of  potassium  in  another  250  c.c.  of  water — 
by  boiling;  mix  the  two  hot  solutions,  when  a  precipitate  of  the  red  per- 
iodide of  mercury  forms,  which  redissolves  in  the  excess  of  iodide  of 
potassium  present;  add  a  cold  saturated  solution  of  corrosive  sublimate 
until  a  precipitate  of  red  periodide  just  begins  to  remain  permanently; 
raise  to  the  boiling-point,  and  the  precipitate  will  possibly  be  dissolved; 
allow  the  solution  to  become  cold,  or  cool  under  the  tap  in  a  suitable 
vessel,  and  decant  from  any  precipitate ;  then  dissolve  120  grammes  of  caustic 
potash  in  about  400  c.c.  of  water;  and  cool  this  solution;  mix  the  two  cold 
solutions,  and  make  up  to  i  litre  of  Nessler's  reagent  with  water.  Ammonia- 
free  water  must  be  used  throughout. 

77 


78  LABORATORY   WORK 

The  reagent  should  be  kept  in  a  tight-fitting  glass-stoppered  store  bottle, 
and  small  quantities  emptied  out  into  a  smaller  one  for  use  from  time  to 
time.     It  is  most  sensitive  after  it  has  been  kept  for  some  time. 

3.  A  strongly  alkaline  solution  of  the  permanganate  of  potassium; 
which  should  alwaj's  be  boiled  for  a  few  minutes  prior  to  use,  in  order  to 
get  rid  of  any  traces  of  ammonia. 

The  amounts  recommended  to  be  used  in  making  up  the  stock  solution 
are — 

Caustic  potash,  200  grammes. 
Permanganate  of  potassium,  8  grammes. 
Ammonia-free  distilled  water,  to  i  litre. 

Ammonia-free  distilled  water  may  be  made  by  distilling  tap  water, 
after  first  fixing  the  ammonia  present  by  the  addition  of  a  drop  or  two 
of  dilute  sulphuric  acid ;  the  distillate  from  the  bulk  of  a  litre  of  the  water 
can  then  be  collected  as  "  ammonia-free."  As  the  previously  ammonia- 
free  water  is  very  liable  to  take  up  traces  of  ammonia,  it  should  always  be 
carefully  tested  prior  to  use,  and  any  trace  of  ammonia  present  must  be 
distilled  off. 

Special  Apparatus  required : 

Six  Nessler  glasses.  These  are  narrow  cylinders,  each  marked  off  at  a 
point  which  indicates  the  level  to  which  50  c.c.  of  water  will  stand  in  them; 
they  should  be  made  of  thin  colourless  glass,  and  of  precisely  siniilar 
diameter. 

Condensing  apparatus,  as  shown  in  Fig.  14.  The  small  tube  perforating 
the  stopper  of  the  boiling-flask  is  seen  to  be  surrounded  in  the  greater  part 
of  its  length  by  a  larger  tube.  A  constant  circulation  of  cold  water  in  the 
space  between  these  tubes  causes  a  condensation  of  the  vapour  which 
arises  from  the  boiling  water,  this  distillate  being  received  into  Nessler 
glasses. 

A  white  porcelain  slab,  6  inches  by  4  inches. 

A  mounted  graduated  burette. 

A  2  c.c.  pipette 

The  Process. 

The  amount  of  "free  and  saline  ammonia  "  is  first  estimated — 
i.e.,  that  ammonia  which  exists  in  solution  in  the  water,  or  in 
combination  with  acids  (carbonic,  nitric,  etc.),  or  in  some  other 
easily  decomposable  form. 

The  Nessler  reagent  will  create  the  faintest  possible  evidence 
of  a  yellow  colour  in  50  c.c.  of  the  sample  when  this  contains 
only  a  very  small  amount  of  "  free  ammonia."  It  is  well  to 
make  it  a  practice  to  test  the  water  in  this  waj'  before  com- 
mencing Wanklyn's  process,  in  order  to  know  whether  the  sample 
contains  Httle  or  much  "  free  and  saline  "  ammonia.  If  more 
than  a  faint  yellow  tint  forms,  the  water  should  be  diluted, 
as  it   may  otherwise  be  difficult   to  get  the  large  amount  of 


wanklyn's  process 


79 


8o  LABORATORY    WORK 

ammonia  over  and  to  match  it.  For  instance,  in  the  case  of 
extremely  foul  waters,  the  degree  of  colour  due  to  the  ammonia 
in  the  first  50  c.c.  of  distillate  is  too  intense  to  be  matched  by 
the  standard  solution,  for  in  many  cases  a  copious  precipitate 
appears  and  it  is  impossible  to  make  a  comparison.  In  such 
cases,  smaller  quantities  of  the  original  water  should  be  diluted 
with  an  equal  bulk,  and  sometimes  even  with  five  or  ten  times 
its  amount,  according  to  the  depth  of  yellow  colour  obtained, 
of  distilled  ammonia-free  water,  prior  to  distillation. 

1.  The  condenser  is  hable  to  become  contaminated  with 
ammonia.  Therefore  first  distil  some  clean  water  through  the 
apparatus  until  the  distillate  gives  no  colour  with  Nessler's 
reagent. 

2.  Five  hundred  c.c.  {i.e.,  half  a  litre)  of  the  water  are  placed 
within  a  boiUng-flask. 

If  the  water  is  acid  or  even  neutral,  a  little  pure  anhydrous 
sodium  carbonate  should  be  added  so  as  to  ensure  alkalinity. 
The  motive  for  tliis  is  to  enable  the  free  ammonia  to  come  away 
readily,  since  any  acidity  would  exert  a  fixing  influence  upon  it; 
it  also  decomposes  ammonium  sulphate, 

3.  The  boiling-flask  is  then  tightly  connected  to  the  con- 
denser, so  that  no  uncondensed  vapour  can  escape  at  this  point. 
The  Bunsen  burner  is  next  hghted,  the  flame  applied  to  the 
flask,  and  rapid  boiling  is  encouraged. 

4.  The  water-tap  is  turned  to  such  an  extent  that  the  water, 
after  circulating  in  the  outer  tube  of  the  condenser,  flows  in  a 
small  stream  to  the  waste-sink. 

5.  A  Nessler  glass  is  placed  so  as  to  catch  the  distillate,  and 
when  sufficient  of  this  is  collected  so  as  to  reach  up  to  the  level 
of  the  50-c.c.  mark,  a  second  glass  is  substituted,  and  then  a 
third. 

6.  When  three  Nessler  glasses  are  thus  filled  up  to  their  50-c.c. 
marks  with  distillate,  a  fourth  is  placed  to  catch  more  of  the  dis- 
tillate, while  2  c.c.  of  Nessler's  reagent  are  added  to  each  of  the 
three  glasses.  If  these  glasses  be  placed  upon  a  white  porcelain 
slab  from  left  to  right  in  the  order  in  which  they  received  the 
distillate,  the  yellow  colour  furnished  in  each  of  them  by  the 
reagent  will  show  a  decrease  in  amount  from  left  to  right,  since 
the  first  50  c.c.  collected  will  contain  tlie  most  "  free  and  saline 
ammonia,"  and  the  third  the  least. 

7.  The  gas  may  be  turned  out  and  the  distillation  stopped  if 


wanklyn's  process  ^^ 

there  is  no  colour  in  the  third  Nesslcr  glass,  or  if  it  be  extremely 
faint,  since  all  the  "  free  and  saUne  ammonia  "  will  then  have 
come  over.  If,  however,  the  colour  is  distinct  in  the  third 
Nessler  glass  of  distillate,  a  fourth  must  be  collected  andtested 
with  2  c.c.  of  the  reagent,  and  even  a  fifth  may  be  occasionally 
necessary.  It  is,  of  course,  imperative  that  all  the  ree  and 
saline  ammonia  "  in  the  original  500  c.c.  of  water  shall  be  re- 
moved, and  it  is  seldom  in  a  drinking-water  that  150  c.c.  ot 
distillate  does  not  contain  the  whole  of  this. 

8  The  amount  of  ammonia  must  be  determined  by  matching 
the'colour  in  each  glass.  To  make  this  match  it  is  necessary  to 
take  another  Nessler  glass,  and  to  deliver  into  it  by  a  burette 
the  amount  of  ammonium  chloride  standard  solution  that  is 
iudged  necessary  to  effect  the  match;  the  cylinder  is  then  filled 
up  to  the  50  c.c.  mark  with  distilled  ammonia-free  water,  and 
then  2  c.c.  of  Nessler's  reagent  are  added.  If  the  match  is  not 
correct,  then  a  fresh  comparison  must  be  made  with  more  or  less 
of  the  standard  solution,  as  the  case  may  be.  A  very  httle 
experience  will  enable  the  operator  to  effect  this  matching  with 

great  rapidity,  .    . 

Notes  -It  is  pointed  out  by  Wanklyn  that  it  is  not  necessary 
to  match  each  glass  separately,  since  three-quarters  of  the  total 
amount  of  "  free  and  saline  ammonia  "  is  contained  m  the  hrst 
glass  of  distillate.  OccasionaUy,  however,  there  is  a  famt  dis- 
crepancy between  the  amount  thus  calculated  and  that  obtained 
by  matching  each  glass;  this  may  be  due  to  differences  m  the 
degree  of  alkaUnity  of  waters  and  in  the  rate  of  boihng.  On 
this  account,  and  for  the  reason  that  the  statement  does  not 
hold  true  with  very  foul  waters,  it  is  preferable  m  every  case 
to  estimate  the  amount  of  ammonia  in  each  glass. 

In  every  case  when,  after  stirring  with  a  clean  glass  rod,  the 
colour  in  the  comparison  cyhnder  is  found  to  approach  that  m 
the  distillate,  the  operator  should  cover  up  the  cyhnder  and 
wait  about  three  minutes  before  adding  more  standard  solution, 
since  the  colour  deepens  a  Httle  upon  standing. 

The  presence  and  degree  of  coloration  must  always  be  judged 
by  looking  down  through  the  depth  of  the  water  on  to  a  white 
slab  and  care  must  be  taken  that  the  bottoms  of  the  glasses  and 
the  upper  surface  of  the  slab  are  perfectly  dry,  as  a  thm  layer 
of  intervening  water  diminishes  materially  the  depth  of  colour, 

and  leads  to  error  in  matching. 

6 


82  LABORATORY   WORK 

9.  Having  thus  effected  a  colour  match  by  placing  the  two 
glasses  side  by  side  upon  the  white  slab  under  exactly  the  same 
conditions  of  light  access,  the  amount  of  ammonium  chloride 
solution  which  has  been  used  to  effect  this  is  noted,  and  the 
ammonia  which  this  is  equivalent  to  will  be  the  amount  of  the 
"  free  and  saline  ammonia  "  in  the  glass  of  distillate. 

Example. — One  hundred  and  fifty  c.c.  of  distillate  were  col- 
lected, and  the  last  50  c.c.  are  found  to  contain  no  trace  of 
ammonia.  The  whole  of  the  "  free  and  saline  ammonia  "  in 
the  500  c.c.  of  water  was  therefore  collected  in  two  Nessler 
glasses. 

It  was  necessary  to  add  3  c.c.  of  the  standard  solution  of 
ammonium  chloride  to  the  comparison  test-glass  in  order  to 
match  the  colour  in  the  glass  containing  the  first  50  c.c.  of 
distillate,  and  i  c.c.  of  the  standard  solution  was  required  to 
match  the  colour  in  the  second  50  c.c.  of  distillate. 

The  total  amount,  then,  of  "  free  and  saline  ammonia  "  in 
the  500  c.c.  of  water  corresponds  to  the  ammonia  present  in 
4  c.c.  of  the  standard  solution  of  ammonium  chloride. 

But  I  c.c.  of  this  standard  solution  contains  o-oi  milhgramme 
of  ammonia.     .'.4  c.c.  contains  0-04  milligramme  of  ammonia. 

.•.  there  is  0-04  milligramme  of  "free  and  saline  ammonia" 
in  the  500  c.c.  of  water  (or  500,000  miUigrammes), 

.'.  there  is  o-oo8  milligramme  of  "  free  and  saline  ammonia  " 
in  100  c.c.  (100,000  milligrammes)  of  water,  or  o-oo8  part  per 
100,000. 

10.  The  next  step  in  the  process  is  to  continue  the  distillation 
more  slowly  after  adding  50  c.c.  of  the  recently  boiled  alkaline 
solution  of  permanganate  of  potassium  to  the  boiling- flask;  to 
collect  the  distillate  in  three  Nessler  glasses;  and  to  repeat  the 
process  of  "  Nesslerizing  "  precisely  as  before.  The  ammonia 
now  obtained  is  called  "  albuminoid  ammonia,"  since  it  is  derived 
from  the  breaking  up  of  albuminoid  and  other  nitrogenous 
organic  matter  by  means  of  the  alkaline  permanganate.  It  is 
important  to  remember  that  this  albuminoid  ammonia  comes 
over  more  slowly  and  much  less  evenly  (the  second  Nessler 
glass  sometimes  containing  almost  as  much  as  the  first),  so  that 
the  first  50  c.c.  of  distillate  must  never  be  taken  to  contain 
three-quarters  of  the  total  "  albuminoid  ammonia." 

Example. — It  was  necessary  to  distil  over  200  c.c.  in  four 
Nessler  glasses  before  all  the  ammonia  had  come  over.     The 


wanklyn's  process   '  S^ 

fourth  glass  of  distillate  had  colour  equal  to  that  furnished  by 
0-2  c.c.  of  the  standard  solution,  the  third  to  o-8  c.c,  the  second 
to  3  c.c,  and  the  first  to  2-5  c.c. 

.-.  (o-2  +  o-8  +  2  +  2-5)  =  5-5  c.c.  of  the  standard  solution  were 
required  to  match  the  colour  furnished  by  the  "  albuminoid 
ammonia  "  in  500  c.c.  of  water. 

But  each  c.c.  of  the  standard  solution  =  o-oi  mihigramme  of 
NH3.     .•.  5-5  c.c.  =  0-055  milligramme  of  NH3. 

,'.  there  is  0-055  milligramme  of  HN3  ("  albuminoid  ")  in 
500,000  milligrammes  of  water,  or  o-oii  milligramme  in  100,000 
of  water. 

Conclusions  to  he  Drawn  from  the  Amount  Estimated. — In  the 
case  of  contamination  with  animal  matter  the  "  free  "  ammonia 
exceeds  the  "albuminoid";  while  vegetable  matter  furnishes 
"  albuminoid  "  ammonia  and  practically  no  "  free."  Therefore 
much  "  albuminoid "  along  with  a  very  small  amount  of 
"  free  "  ammonia  indicates  vegetable  contamination,  and  this 
indication  gains  further  support  if  there  is  no  excess  of 
chlorides  and  of  nitrates.  Relatively  high  "  free  "  ammonia 
along  with  "  albuminoid  "  ammonia  above  0-005,  and  excess 
of  chlorine  (and  often  of  oxidized  nitrogen)  will  denote  recent 
animal  pollution. 

If  the  "  albuminoid  "  ammonia  exceeds  0-005  part  per  100,000, 
the  "  free  "  should  be  below  this  amount;  but  if  the  albuminoid 
ammonia  is  much  below  this,  then  a  high  figure  of  "free" 
ammonia  is  probably  due  to  a  reduction  of  nitrates,  and  not  to 
recent  animal  contamination.  Conversely,  if  there  is  practi- 
cally no  "  free  "  ammonia — i.e.,  0-002  or  less — then  the  "  albu- 
minoid "  ammonia  may  be  allowed  to  exceed  o-oi,  as  it  is  evident 
that  the  organic  matter  present  is  purely  vegetable. 

It  may  be  said  that  if  the  free  ammonia  in  upland  surface 
waters  exceeds  0-002,  a  suspicion  of  animal  contamination  is 
warranted. 

"Free"  ammonia,  accompanied  by  practically  no  "albu- 
minoid," is  found  in  the  following  circumstances: 

{a)  The  water  has  been  in  contact  with  a  stratum  contain- 
ing a  reducing  agent  (greensand  contains  a  reducing 
salt  of  iron)  which  has  decomposed  the  oxidized 
nitrogen  originally  present  in  the  water;  or  metal 
pipes,  cement,  etc.,  with  which  a  well-water  has  come 
in  contact  may  effect  this  reduction  to  a  less  extent. 


84  LABORATORY   WORK 

{b)  Other    waters    containing    iron    frequently    possess    a 
marked  amount  of  ammonia  derived  from  the  reduc- 
tion of  nitrates, 
(f)  The   water   has   percolated   a   deposit   in   which   some 

ammonia  salt  is  present. 
(d)  The  sample  is  rain-water,  collected  in  town  districts,  in 
which  ammonia  may  exist  in  considerable  quantities. 

Other  steps  of  the  analysis  will  serve  to  indicate  the  source  of 
"free  ammonia";  and  where  it  is  not  derived  from  organic 
pollution  the  "  albuminoid  ammonia  "  \\dll  always  be  very  low 
indeed. 

If,  in  spite  of  the  previous  dilution,  the  ammonia  in  the  first 
Nessler  glass  of  distillate  still  furnishes  too  deep  a  colour  to 
admit  of  a  satisfactory  match,  the  whole  of  the  distillates  con- 
taining free  ammonia  may  be  mixed  together,  and  the  ammonia  in 
50  c.c.  of  the  light-coloured  mixture  Nesslerized  and  estimated; 
and  from  the  amount  found  in  this  measured  part  the  amount 
in  the  whole  distillate  may  be  calculated. 

Sometimes  while  extracting  the  "  albuminoid  ammonia  "  the 
contents  of  the  boihng-flask  boil  too  violently,  and  "  bumping  " 
ensues;  to  obviate  this  a  gentle  shaking  of  the  flask  will  often 
suffice,  but  in  default  a  few  fragments  of  freshly  ignited  pumice- 
stone  afford  an  excellent  remedy.  The  foulest  waters  and  those 
containing  much  saline  matter  are  most  apt  to  bump,  and  it  is 
highly  important  to  prevent  this,  since  uncondensed  vapour 
thereby  escapes  at  the  distal  end  of  the  tube,  and  sometimes 
some  of  the  water  is  shot  over  from  the  boiling-flask,  both  of 
which  occurrences  obviously  vitiate  the  results.  When  some  of 
the  water  to  which  the  alkaline  permanganate  has  been  added 
thus  spurts  over  into  the  Nessler  glass  placed  to  collect  the 
distillate,  it  is  of  course  impossible  to  "  Nesslerize,"  since  the 
distillate  has  a  pink  colour.  There  is  no  alternative  then 
but  to  pour  back  the  distillate  into  the  flask  and  renew  the 
distillation. 

When  the  "  albuminoid  ammonia"  comes  over  so  slowly  (as 
in  some  peaty  waters)  that  almost  all  the  water  in  the  retort 
threatens  to  be  used  up,  200  c.c.  of  ammonia-free  water  may  be 
added  to  the  flask  and  the  distillation  continued.  In  those  rare 
cases  where  "  the  free  ammonia  "  continues  to  come  over  in 
small  quantities,  it  is  a  good  plan  to  adopt  the  measure  (Rich) 
of  starting  the  process  afresh,  "  Nesslerizing  "  the  first  50  c.c, 


wanklyn's  process  85 

and  then  returning  the  rest  of  the  distillate  to  the  flask,  and 
redistilling  it  before  "  Nesslerizing." 

Strange  to  say,  though  urea  is  decomposed  by  the  boiling  with 
the  alkahne  permanganate,  its  decomposition  does  not  yield 
any  ammonia,  and  this  at  first  sight  would  seem  a  grave  defect 
in  the  process.  When,  however,  it  is  considered  that  this  is 
probably  the  only  nitrogenous  contamination  of  animal  origm 
with  which  a  water  is  hable  to  be  polluted  which  does  not, 
in  the  circumstances,  yield  ammonia,  and  that  urea  in  urine 
naturally  becomes  very  rapidly  changed  into  ammonium  car- 
bonate and  as  such  is  detected  in  the  sahne  ammonia,  the  matter 
is  not  one  of  importance. 

By  Wanklyn's  process  only  about  one-half  of  the  nitrogen  in 
organic  combination  is  liberated  as  "  albuminoid  ammonia  " ;  but 
it  is  not  necessary  that  in  the  process  the  total  nitrogen  contained 
in  organic  matter  should  be  evolved  as  ammonia,  so  long  as  that 
which  is  evolved  gives  an  index  which  bears  a  fairly  fixed  and 
constant  ratio  to  the  total  amount;  so  that  from  this  index  an 
empirical  standard  of  purity  can  be  formed.  The  process  efficiently 
meets  this  requirement. 

When  but  httle  water  remains  in  the  boiling-flask,  the  flame 
must  be  lowered,  as  the  naked  flame  must  not  be  allowed  to 
play  upon  the  glass  above  the  water-level. 

The  presence  of  considerable  sulphuretted  hydrogen  in  water 
interferes  with  Nesslerization ;  this  must  therefore  first  be 
remedied  before  the  free  and  sahne  ammonia  are  distilled  over 
and  estimated,  in  the  following  manner:  The  ammonia  should 
be  fixed  with  10  c.c.  of  normal  sulphuric  acid;  then  if  100  c.c. 
of  the  water  are  distilled  over,  this  amount  of  distillate  will 
contain  all  the  sulphuretted  hydrogen.  The  water  remaining 
in  the  boihng-flask  is  then  neutralized  with  10  c.c.  of  normal 
sodic-hydrate,  when  Wanklyn's  process  can  be  performed. 

When  it  is  found  necessary  so  to  deal  with  sulphuretted 
hydrogen,  a  blank  experiment  should  be  performed,  by  which 
any  ammonia  found  in  500  c.c.  of  ammonia-free  distilled  water 
containing  10  c.c.  of  normal  sulphuric  acid  and  10  c.c.  of  normal 
sodic-hydrate  is  distilled  over  and  estimated,  and  this  is  deducted 
in  arriving  at  the  figure  of  the  free  and  sahne  ammonia  in  the 
sample. 


CHAPTER  XI 

THE  OXIDIZABLE  ORGANIC  MATTER— E.  FRANKLAND'S 
PROCESS 

In  the  presence  of  organic  matter  the  permanganate  of  potassium, 
under  favourable  conditions,  will  part  with  oxygen  until  all  the 
permanganate  has  become  reduced  to  hydrated  manganese 
dioxide,  as  indicated  by  the  loss  of  the  original  pink  colour. 

While  a  certain  proportion  of  the  organic  matter  present  in 
water  is  always  oxidizable  by  the  permanganate  of  potassium, 
this  varies  with  the  nature  of  the  organic  pollution,  and  it  there- 
fore bears  no  constant  ratio  to  the  total  quantity  of  such  pollution 
present.  Some  forms  of  animal  matter  reduce  less  perman- 
ganate than  others,  and  comparatively  harmless  peaty  waters 
may  absorb  much  more  ox^^gen  than  waters  dangerously  polluted 
with  animal  matter. 

Despite  these  drawbacks,  and  the  fact  that  in  Wanklyn's 
process  we  possess  the  means  of  making  a  far  closer  estimation 
of  organic  matter,  the  test  under  consideration  frequently 
furnishes  corroborative  e\ddence  of  value,  but  it  is  most  service- 
able as  a  means  of  gauging  the  comparative  purity  of  a  series 
of  waters,  or  of  the  same  water  from  time  to  time. 

A  two-hours'  exposure  of  the  water  to  the  permanganate  is 
quite  short  enough  for  the  test  to  be  of  much  value,  since  it  is 
chiefly  the  putrescent,  or  very  easily  reducible  organic  matter, 
which  is  oxidized  in  the  first  half-hour.  There  is  little  or  no 
advantage,  however,  in  making  the  test  extend  to  four  hours. 
It  must  be  clearly  understood  that  even  at  the  end  of  four  hours 
the  oxidation  of  the  more  stable  organic  matter  by  acid  per- 
manganate would  be  incomplete;  and  so  the  two-hours'  test  is 
generally  adopted  for  the  purpose  of  obtaining  a  standard  or 
figure  for  comparison. 
The  conduction  of  the  process  at  a  precise  temperature  has 

86 


THE   OXIDIZABLE   ORGANIC   MATTER  ^7 

been  proved  by  experiment  to  be  an  important  factor  for  the 
amount  of  oxygen'taken  from  the  permanganate  vanes  con- 
siderablv  at  different  temperatures.  ,-,       f 

If  Jwater  is  bottled  long  before  analysis,  the  quanWy  o 
oxygen  absorbed  frequently  increases;  this  is  due  to  the  fact  that 
r  organic  matter  is  slowly  passing  into  less  stable  forms   and 
is  therefore  less  resistant  to  the  permanganate),  and  rarely  . 
may  also  result  from  a  reduction  of  nitrates  by  organic  matter 
(bacteria,  etc.)  to  nitrites. 

Tidy's  Modification  of  the  Forchammer  Process. 
Special  Reagents  required : 

I.  A  standard  solution  of  the  permanganate  of  potassium  lo  c.c  of 
which  contain  i  milligramme  of  available  oxygen;  made  by  dissolving 
which  contain  ^  "       ^  ^.^      ^^  distilled  water  which  has 

SfSy"  n°/.dtir;:iman  "nate  solution  to  oxidise  any  impurities 
been  larntiy       5  ^^^j^ble,  and  must  be  frequently  renewed. 

^ri-Jhly  prepared  solution  of  potassium  iodide,  made  by  dissolvmg 
nnp  Dart  of  the  pure  salt  in  ten  of  distilled  water. 

°C«te  sulphuric  acid  (r  in  3);  a  solution  of  tire  P«ga„ate  o 
potassium  is  dropped  in  until  a  faint  pinlr  tint  remains  after  four  hours 

^*riTo!utrof':Sium  thiosulphate,  made  by  dissolving  t    gramme 
of  the  crystallized  salt  in  a  litre  of  distilled  water. 

r  A  freshly  prepared  solution  of  starch,  made  by  adding  0-5  gramme  of 
wen-washed  ItLS  to  .00  c.c.  of  cold  distilled  water,  and  ^^^Y^^^^^ 
for  five  minutes;  then  let  settle  and  decant  the  almost  clear  supernatant 
liquid. 

Special  Apparatus  required : 

Two  thin  glass-stoppered  bottles  or  flasks  of  only  a  little  more  than 

100  c.c.  capacity.  ^       .       j         1 

Two  thermometers  graduated  on  the  Centigrade  scale 

Graduated  burettes;  glass  stirring  rods;  white  porcelam  slabs. 

The  Process. 

I    To  100  c  c  of  the  water  in  one  of  the  thin  glass  flasks  add 
of  the  dilute  acid;  then  add  10  c.c.  of  the  standard  solu- 


10  c.c 


tion  of  permanganate,  and  insert  the  stopper. 

2  The  solution  of  thiosulphate  is  unstable,  and  it  is  therefore 
advisable  to  always  include  a  control  test  as  follows:  100  c  c. 
of  cold  recmtly  boiled  distilled  water  are  treated  m  precisely  the 


same  manner. 


88  LABORATORY   WORK 

3.  Place  both  flasks  in  a  hot-water  o\'en  kept  at  a  constant 
temperature  of  about  27°  C,  this  being  a  temperature  which 
facilitates  the  parting  of  the  oxygen  from  the  permanganate  of 
potassium. 

In  the  presence  of  organic  matter  live-eighths  of  the  oxygen 
is  liberated  from  the  permanganate  in  the  following  manner: 

KaMugOg  -1-  3H2SO4  +  oxidizable  matter  =  2MnS04  + 
K2S04-i-3H20-f  5O  (combined  with  oxidizable  matter). 

The  amount  of  sulphuric  acid  added  in  the  process  is  not 
sufficient  to  make  the  permanganate  part  with  its  oxygen,  but 
merely  to  assist  it  in  doing  so  in  the  presence  of  oxidizable 
organic  matter. 

4.  After  two  hours  remove  the  flasks  from  the  oven,  and 
proceed  to  estimate  the  amount  of  iindecomposed  permanganate. 
Add  a  drop  or  two  of  the  solution  of  iodide  of  potassium,  stirring 
well  with  a  clean  glass  rod;  when  the  pink  colour  is  entirely 
replaced  by  a  yellow  one  (due  to  free  iodine).  The  undecom- 
posed  permanganate  immediately  reacts  upon  the  iodide,  with 
the  result  that  an  amount  of  free  iodine  is  liberated  proportionate 
to  the  amount  of  undecomposed  permanganate,  according  to 
the  following  equation: 

KaMngOg  +  loKI  +  8H2S04=  2MnS04  +  6K0SO4  + 
8H20+5I2- 

5.  The  next  step  is  to  ascertain  the  value  of  this  free  iodine 
in  terms  of  sodium  thiosulphate.  Add  by  a  graduated  burette 
the  standard  solution  of  sodium  thiosulphate  until  the  yellow 
colour  has  almost  completely  disappeared — i.e.,  very  little  free 
iodine  remains ;  and  so  as  to  estimate  the  remaining  trace  with 
greater  precision,  create  the  blue  colour  of  the  iodide  of  starch 
by  adding  a  drop  or  two  of  starch  solution,  then  resume  the 
addition  of  the  standard  solution  of  sodium  thiosulphate  until 
this  blue  colour  has  just  disappeared.  The  reaction  of  the  thio- 
sulphate solution  with  the  free  iodine  is  according  to  the  following 

equation: 

2Na2S203  + 12  =  2NaI  -1-  Na2S406. 

If  this  process  of  decoloration  has  been  properly  performed,  and 
if  the  necessary  amount  of  thiosulphate  solution  has  not  been 
exceeded,  a  drop  of  the  permanganate  solution  will  suffice  to 
restore  the  blue  colour  to  the  water. 


THE    OXIDIZABLE    ORGANIC    MATTER  89 

6.  When  we  come  to  similarly  estimate  the  free  iodine  of  the 
control  test  in  terms  of  the  thiosulphate  solution,  the  quantity 
of  the  latter  used  will  be  the  amount  which  is  equivalent  to  10  c.c. 
of  the  standard  solution  of  permanganate  (containing  i  milli- 
gramme of  available  oxygen).  The  difference,  therefore,  between 
the  amount  of  thiosulphate  solution  here  required  and  that 
required  to  titrate  the  amount  of  free  iodine  liberated  by  the 
permanganate  in  the  sample  of  water,  will  represent  the  amount 
of  permanganate  decomposed. 

Example. — ^The  distilled  water +10  c.c.  of  permanganate  used 
up  26-5  c.c.  of  the  thiosulphate  solution. 

.-.  26-5  c.c.  of  the  thiosulphate  solution  may  be  considered  as 
equivalent  to  10  c.c.  of  permanganate,  or  the  i  milligramme  of 
oxygen  which  this  will  part  with. 

The  sample  water  +  10  c.c.  of  permanganate  required  only 
24-5  c.c.  of  the  thiosulphate  solution,  and  therefore  an  amount 
of  oxygen  equivalent  to  26-5 -24-5  =  2-0  c.c.  of  thiosulphate 
solution  has  been  taken  up  by  the  organic  matter.  But  if 
26-5  c.c.  of  thiosulphate  solution  is  equivalent  to  i  milligramme 
of  oxygen,  then  2-0  c.c.  =  0-075  milligramme  of  oxygen. 

.•.  0-075  milligramme  of  oxygen  is  taken  up  by  100  c.c.  of 
water  (100,000  milligrammes);  or  the  oxidizable  organic  matter 
in  a  hundred  thousand  parts  of  water  required  0-075  part  of 
oxygen  to  oxidize  it  in  two  hours  at  27°  C. 

Notes. — It  is  essential  to  bear  in  mind  the  important  fact  that 
there  are  other  substances  which  water  is  liable  to  contain  which 
will  reduce  the  permanganate  besides  organic  matter  —  i.e., 
nitrites,  ferrous  salts,  and  sulphur  compounds  other  than  sul- 
phates— so  that  it  is  necessary  to  dispose  of  or  account  for  these 
before  attributing  the  reduction  in  the  permanganate  solely  to 
oxidizable  organic  pollution.  Since  as  little  as  |  grain  to  the 
gallon  of  iron  can  be  detected  by  the  chalybeate  taste  which  it 
imparts  to  the  water,  in  the  absence  of  any  such  taste  the  pres- 
ence of  iron  may  be  disregarded.  If,  however,  iron  is  markedly 
present  as  a  ferrous  salt,  one  may  deduct  from  the  total  ox3^gen 
consumed  the  amount  necessary  to  convert  the  iron  into  the 
ferric  condition  (112  parts  of  iron  in  a  ferrous  form  will  require  to 
this  end  16  parts  of  oxygen).  To  get  rid  of  the  nitrous  acid  and 
sulphur  compounds  other  than  sulphates,  it  is  necessarj'  to  boil 
the  water  after  acidulation  with  the  sidphuric  acid  for  about 
twenty  minutes.     Then  it  is  made  up  to  the  original  bulk  with 


90 


LABORATORY   WORK 


distilled  water,  allowed  to  cool  to  27°  C,  and  the  test  is  then 
proceeded  ^^dth  as  above. 

The  amount  of  permanganate  added  must  always  be  sufficient 
to  leave  a  distinct  pink  colour  at  the  end  of  the  heating.  There- 
fore, in  some  foul  waters  it  is  necessary  to  make  further  addi- 
tions of  the  permanganate  solution,  carefully  noting  the  total 
amount  which  has  been  employed.  The  calculation  is  facilitated 
if  in  these  cases  the  same  amount  is  added  to  the  control  flask. 

At  the  end  of  the  process — i.e.,  after  titration — the  blue  colour 
returns  when  the  fluid  has  been  exposed  a  few  minutes  to  the  air. 

Conclusions  to  be  Drawn  from  the  Amount  Estimated. — In  very 
pure  waters  the  oxygen  thus  absorbed  in  two  hours  is  below 
0-05  part  per  100,000;  but  a  figure  not  exceeding  o-i  is  not  un- 
favourable to  the  water's  purity.  Even  when  the  latter  figure 
is  exceeded  no  definite  conclusion  can  be  come  to  unless  the 
nature  of  the  organic  pollution  is  known,  since  a  peaty  water 
would  not  necessarily  be  judged  as  harmful  even  if  it  required 
three  or  four  times  this  amount  of  oxygen  to  oxidize  its  vegetable 
organic  matter. 

The  following  table  of  approximate  standards  for  this  process 
was  drawn  up  by  Frankland  and  Tidy : 

Amounts  of  Oxygen  Absorbed  by  100,000  Parts  of  Water. 


Derived  from  Upland 
Surfaces. 

Derived  from  Sources 

other  than  Upland 

Surfaces. 

Water     of     great    organic 

purity 
Water  of  medium  purity  .  . 
Water   of  doubtful  purity 
Polluted  water 

Not  more  than  o-i 
0-3 

^love  than            0-4 

Not  more  than  0-05 
0-15 

More  than            0-2 

1 

E.  FRANKLAND 'S  PROCESS 

A  short  reference  only  to  this  ingenious  process  is  here  given, 
since  it  is  too  difficult  and  complex  for  any  but  trained  chemists 
to  perform,  and  it  is  generally  held  that  Wanklyn's  method 
attains  to  as  true  an  estimate  of  the  organic  matter  at  the  cost 
of  far  less  trouble ;  and  as  regards  the  opinion  which  the  results 
enable  one  to  form  upon  the  water,  it  closely  coincides  with  that 
formed  when  the  same  water  is  analyzed  by  Wanklyn's  method. 
The  process  has  been  employed  in  certain  official  analyses,  and 


E.  frankland's  process  91 

the  public  health  student  should  understand  the  significance 
of  the  terms  used  to  express  results. 

As  pointed  out  on  a  previous  page,  the  rationale  of  the  method 
is  as  follows:  When  water  is  evaporated  to  dryness,  and  the 
residue  is  burnt  with  the  oxide  of  copper,  the  nitrogen  and  the 
carbon  which  result  from  the  combustion  of  the  organic  matter 
can  be  collected  and  estimated  as  "  organic  nitrogen  "  and 
"  organic  carbon."  Steps  are  taken,  of  course,  to  ehminate 
the  nitrogen  and  carbon  which  are  not  present  in  the  form  of 
organic  matter. 

The  chief  objections  raised  against  the  process  are  that  it  is 
tedious,  costly,  and  difficult  of  performance.  Inferences  are  drawn 
from  the  ratio  which  "  organic  nitrogen  "  bears  to  "  organic 
carbon,"  while  the  amount  of  the  former  is  less  reliably  estimated 
than  that  of  the  latter.  Dupre  points  out  that  sea-water  shows 
a  ratio  between  the  two  worse  even  than  is  found  in  pure  sewage. 

By  this  process  the  purity  of  water  is  judged  from  a  considera- 
tion of  the  actual  amounts  of  organic  carbon  and  organic  nitrogen 
present  and  their  relative  proportions  to  each  other;  and  both  a 
low  quantity  of  each  and  a  small  relative  amount  of  organic 
nitrogen  to  carbon  is  favourable  to  the  water.  Much  C  and 
little  N  is  indicative  of  vegetable  pollution;  whereas,  if  the 
relative  proportion  of  N  to  C  is  high,  the  inference  is  that  the 
pollution  is  largely  of  animal  origin. 

The  Rivers  Pollution  Commissioners  held  that  "  a  good  drink- 
ing-water should  not  yield  more  than  0-2  part  of  organic  carbon, 
or  0-02  of  organic  nitrogen  in  100,000  parts."  They  found  that 
in  peaty  waters  the  ratio  of  nitrogen  to  carbon  was  i  :  ii-g,  while 
in  similar  waters  that  had  been  stored  in  lakes  the  nitrogen  to 
carbon=i  :  5-9.  In  sewage  the  average  of  a  large  number  of 
samples  gave  nitrogen  to  carbon  =  i  :  2-1.  Highly  polluted  well- 
waters  gave  nitrogen  to  carbon  =  i  :  3-1. 


CHAPTER  XII 

OXIDIZED  NITROGEN  (NITRATES  AND  NITRITES) 

Nitrates  and  nitrites  in  water  represent  the  oxidized  nitrogen 
derived,  in  the  main,  from  the  decomposition  of  nitrogenous 
organic  matter.  When  organic  matter  undergoes  decomposition, 
much  of  the  N  passes  off  in  the  free  state,  the  remainder  com- 
bining with  hydrogen  to  form  ammonia;  hence  when  "  free  and 
saline  ammonia  "  is  found  in  large  quantities  in  a  water  it  almost 
invariably  affords  evidence  of  the  presence  of  very  recent  organic 
pollution,  such  as  raw  sewage.  As  the  water  continues  on  its 
course,  the  N,  mainly  through  the  action  of  so-called  "  nitrifying 
organisms  "  in  the  soil,  becomes  partially  oxidized  to  nitrous 
acid  (HNO2),  which,  combining  with  bases  (commonly  of  lime 
and  less  often  of  soda  and  potash),  forms  nitrites  ;  therefore  the 
presence  of  these  salts  generally  indicates  recent  organic  pollu- 
tion. The  same  purifjdng  agencies  continuing  to  act,  the 
nitrous  acid  combines  with  more  oxygen,  and  becomes  nitric 
acid  (HNO3),  which  forms  nitrates  of  the  above-mentioned  bases, 
until  ultimately  none  of  the  original  N  may  have  escaped  this 
complete  oxidation. 

When  both  forms  of  ammonia  by  Wanklyn's  process  are  very 
low,  then  practically  the  whole  of  the  organic  matter  may  be 
considered  as  thus  purified;  when  this  is  not  the  case,  however, 
purification  has  only  been  partially  effected.  When,  as  in  some 
rare  cases,  the  water  in  its  subsequent  flow  meets  with  reducing 
agents  (either  inorganic  or  organic),  the  nitrates  which  have 
been  built  up  may  become  gradually  deoxidized,  and  reduced 
through  nitrites  to  ammonia  again;  but  in  these  cases  one  finds 
practically  no  albuminoid  ammonia,  oxidizable  organic  matter, 
etc.,  so  that  the  large  amount  of  free  ammonia  would  not  be 
taken  as  due  to  recent  animal  pollution. 

It  is  necessary,  however,  in  all  cases  where  nitrates  exist, 

92 


OXIDIZED    NITROGEN    (NITRATES    AND    NITRITES)  93 

before  ascribing  their  presence  to  relatively  recent  organic 
pollution  (which  will  be  almost  entirely  of  animal  origin),  to 
preclude  the  possibility  of  their  origin  from  soluble  nitrates 
derived  from  remote  organic  matter  in  the  strata  permeated, 
since  waters  of  great  organic  purity  from  the  chalk,  the  oolite, 
the  red  sandstone  and  the  lias  may  contain  marked  traces. 
It  has  been  suggested  that  these  nitrates  may  sometimes  be 
derived  from  fossil  remains. 

An  appreciation  of  these  facts  enables  a  true  estimate  of 
the  importance  of  the  presence  and  amount  of  nitrates  to 
be  made. 

Thus  nitrites  either  indicate  the  incomplete  nitrification  of 
ammonia,  or  the  reduction  of  nitrates  by  mineral  reducing  agents 
or  microbes;  thus,  when  they  occur  in  shallow  wells  or  rivers 
their  presence  should  suffice  to  condemn  the  water  for  drinking 
purposes,  since  they  would  point  to  the  probability  that  animal 
pollution  is  present  or  very  recent ;  but  when  they  occur  in  deep- 
well  water  they  may  not  denote  present  danger,  for  they  may 
result  from  the  reduction  of  nitrates,  by  iron  in  natural  deposits 
or  even  by  iron  pipes.  Generally  speaking,  the  importance  to 
be  attached  to  their  presence  will  depend  upon  the  results  ob- 
tained from  Wanklyn's  process.  Nitrites  have,  of  course,  a 
tendency  to  become  nitrates,  so  that  whereas  a  water  often  con- 
tains the  latter  without  any  evidence  of  the  former,  nitrates  will 
always  be  found  accompanying  nitrites;  and,  owing  to  their 
instability,  it  is  exceptional  to  find  nitrites  in  polluted  samples 
of  water. 

Nitrates  and  nitrites  exist  only  in  traces  in  waters  vitiated 
by  vegetable  matter  alone,  and  plant  life  tends  to  remove  nitrates 
and  nitrites  from  a  water;  thus  a  polluted  water,  subsequently 
exposed  to  plant  life,  may  furnish  in  its  oxidized  nitrogen  but 
slight  evidence  of  its  previous  pollution. 

Even  when  the  whole  of  the  N  of  sewage  matter  is  fully 
oxidized  to  nitrates,  the  water  must  be  regarded  as  dangerous 
for  drinking  purposes,  for  at  any  time  the  agencies  responsible 
for  the  purification  may  be  overtaxed,  and  dangerous  pollution 
may  pass  unchanged  into  the  water. 

Traces  of  nitrates  are  present  in  almost  all  waters,  including 
rain-water. 


94  LABORATORY   WORK 

Qualitative  Tests  for  Nitrates. 

The  old  brucine  test  in  careful  hands  will  detect  extremely 
faint  traces. 

A  few  drops  of  a  saturated  solution  of  brucine  are  well  mixed 
with  half  a  test-tubeful  of  the  suspected  water;  then,  with 
the  test-tube  held  well  on  the  slant  against  a  white  background, 
pure  sulphuric  acid  is  poured  gently  down  the  side  until  the  acid 
forms  a  distinct  layer  at  the  bottom  of  the  test-tube.  When  the 
test-tube  is  brought  to  the  vertical,  a  pink  zone  is  seen  to  occupy 
the  line  of  junction  between  the  mixture  of  brucine  and  water 
and  the  sulphuric  acid;  the  pink  is  transitory,  however,  and 
soon  changes  to  a  brownish-yellow.  Especially  does  the  colour 
change  quickly  when  the  nitrates  are  liigh  in  amount. 

If  no  coloured  zone  appears,  the  test-tube  should  be  gently 
swayed  to  and  fro,  so  as,  without  mixing  them,  to  bring  more 
of  the  water  and  brucine  in  contact  with  the  sulphuric  acid;  if 
the  results  are  still  negative,  nothing  but  an  insignificant  trace 
of  nitrates  can  be  present. 

A  control  test  should  be  made  with  nitrate-free  water,  in  order 
to  test  the  purity  of  the  sulphuric  acid. 

A  still  more  delicate  mode  of  applying  the  same  test  is  to 
place  5  c.c.  of  the  water  in  a  perfectly  clean  platinum  dish  and 
evaporate  to  dryness.  Then  a  drop  of  pure  sulphuric  acid  is 
allowed  to  fall  into  the  dish,  and  a  minute  crj^stal  of  brucine  is 
added.  A  pink  colour  will  appear  with  an  extremely  faint 
trace. 

The  Diphenylamine  Test. — The  sensitiveness  of  this  test  depends 
greatly  on  the  mode  of  performing  it.  The  reagent  to  be  em- 
ployed is  a  solution  of  diphenylamine  in  sulphuric  acid  and  5  per 
cent,  hydrochloric  acid;  three  or  four  drops  of  this  reagent  are 
added  to  i  c.c.  of  the  liquid  to  be  tested,  then  2  c.c.  of  concen- 
trated sulphuric  acid,  and  the  whole  shaken.  In  the  presence  of 
nitric  acid  or  nitrous  acid  the  mixture  acquires  a  blue  colour. 
When  nitrites  are  present,  the  blue  colour  appears  at  once, 
whereas  it  forms  slowly  when  due  to  nitrates.  No  other  con- 
stituent of  natural  water  gives  a  similar  reaction. 

Most  tests  for  nitrates  are  responded  to  equally  by  nitrites. 
The  brucine  and  sulphuric  acid  test  responds  also  to  nitrites, 
but  not  to  nitrites  in  the  absence  of  nitrates  if  the  acid  is  diluted 
with  an  equal  amount  of  distilled  water. 


OXIDIZED    NITROGEN    (NITRATES    AND    NITRITES)  95 


Qualitative  Tests  for  Nitrites. 

The  old  starch  test  for  nitrites  is  sufficiently  reliable  and  deli- 
cate, when  carefully  performed,  for  most  purposes;  but  there 
must  be  no  sulphuretted  hydrogen  in  the  water.  It  consists  in 
the  addition  of  a  little  clear  starch  solution,  and  a  drop  of  a 
solution  of  potassium  iodide  to  some  of  the  water  in  a  test-tube. 
Dilute  sulphuric  acid  is  then  added,  when  in  the  presence  of 
nitrites  a  dark  blue  tint  appears  immediately  ;  nitrous  acid  being 
liberated  by  the  sulphuric  acid;  it  then  oxidizes  the  potassium 
iodide,  leaving  the  iodine  free  to  combine  with  the  starch  as  the 
hhie  iodide.  The  test  should  be  performed  at  the  lowest  possible 
temperature,  and  an  instant  reaction  must  take  place,  for  nitrates 
give  similar  results  after  standing  awhile. 

Ilosvay's  Naphthylamine  test  is  more  delicate.  The  following 
solutions  are  required: 

{a)  Solution  of  sulphanilic  acid,  0-5  gramme  in  150  c.c.  of 

dilute  acetic  acid  (specific  gravity,  1-04). 
(6)  Solution   of    naphthylamine,  made   by    dissolving   o-i 
gramme  in  20  c.c.  of   distilled  water,   filtering,  and 
adding  150  c.c.  of  dilute  acetic  acid. 

If  I  c.c.  of  each  of  the  above  solutions  be  added  to  50  c.c.  of 
the  suspected  water  in  a  Nessler  glass,  placed  upon  a  white 
porcelain  slab,  a  pink  colour  develops  if  nitrites  are  present.  If 
no  colour  appears  within  fifteen  minutes,  nitrites  may  be  con- 
sidered as  absent. 

This  method  is  sufficiently  sensitive  for  ordinary  purposes ;  but 
the  most  delicate  appreciation  of  nitrites  is  made  by  acidify- 
ing a  large  bulk  of  the  water  with  acetic  acid,  and  then  testing 
a  little  of  the  first  part  of  the  distillate  from  the  water.  If  the 
water  contains  sulphuretted  hydrogen  this  must  first  be  separated 
by  means  of  a  little  well-washed  carbonate  of  lead  and  subse- 
quent filtration. 


The  Quantitative  Estimation  of  Nitrites. 

The  estimation  may  be  based  upon  Ilosvay's  reaction,  the 
degree  of  colour  thereby  furnished  being  matched  by  means  of 
a  standard  solution  of  potassium  nitrite,  in  the  manner  of  the 
colorimetric  estimation  of  lead,  as  previously  described. 


96  LABORATORY   WORK 

The  standaxd  solution  of  potassium  nitrite  is  made  of  the  required 
strength  by  dissolving  i-i  grammes  of  pure  silver  nitrite  in  hot  distilled 
water,  and  then  adding  a  slight  excess  of  potassium  chloride.  This  solution 
is  allowed  to  cool,  and  is  then  made  up  to  i  litre;  the  silver  chloride  is 
allowed  to  settle,  and  each  loo  c.c.  of  the  clear  supernatant  liquid  is 
diluted  to  i  litre;  i  c.c.  of  this  liquid  contains  o-oi  milligramme  of  N  as 
nitrite.  The  solution  should  be  kept  in  the  dark  in  a  number  of  small 
bottles  filled  to  the  level  of  the  stopper. 

The  quantity  of  nitrite  present  is  estimated  by  taking  several 
cylinders  containing  known  amounts  of  standard  nitrite  solution, 
varying,  say,  from  o-02  to  0"i  milligramme  of  N  as  nitrite  in  lOO  c.c. 
of  distilled  water;  and  i  c.c.  of  each  of  the  two  solutions  employed 
in  Ilosvay's  test  must  be  added  to  the  sample  and  comparison 
waters  at  the  same  time,  since  the  colour  gradually  deepens 
upon  standing.  As  the  colour  takes  nearly  a  quarter  of  an  hour 
to  fully  develop,  the  cylinders  should  be  covered  and  set  aside 
for  this  period  before  they  are  compared. 

Example. — The  comparison  cylinder  containing  8  c.c.  of  the 
standard  nitrite  solution  is  found  to  haye  the  same  tint  of  colour 
as  that  produced  by  the  nitrite  in  the  sample,  and  therefore  the 
amount  of  N  as  nitrite  in  the  sample  of  water  is  equivalent  to 
that  contained  in  8  c.c.  of  the  standard  solution. 

But  I  c.c.  of  this=  o-oi  milligramme  of  N  as  nitrite. 

.•.  8  c.c.  =  o-o8  milligramme  of  N  as  nitrite. 

.•.  there  is  o-o8  milligramme  of  N  as  nitrite  in  lOO  c.c.  (or 
100,000  milligrammes)  of  water,  or  O'oS  part  of  N  as  nitrite  in 
100,000  parts  of  water. 

The  starch,  iodide,  and  zinc  reaction  may  also  be  taken 
advantage  of  as  a  means  of  making  a  quantitative  estimation 
on  colorimetric  principles. 

If  the  sample  is  coloured  it  must  be  decolorized  as  much  as 
possible  by  adding  to  200  c.c.  of  the  water,  3  c.c.  of  a  solution  of 
sodic- carbonate  (1:3)  and  i  c.c.  of  soda-lj'e  (1:4);  when  in  most 
waters  the  precipitated  carbonates  of  the  alkaline  earths  carry 
down  with  them  much  of  the  colouring  matter.  If  the  water  is 
soft,  a  few  drops  of  a  solution  of  alum  should  first  be  added. 

As  distilled  water  wiU  often  give  a  reaction  for  nitrite,  care 
must  be  taken  to  see  that  the  distilled  water  employed  in  the 
standard  solution  and  in  the  comparison  cylinders  does  not  so 
react. 


oxidized  nitrogen  (nitrates  and  nitrites)        97 

The  Quantitative  Estimation  of  Nitrates  and  Nitrites. 

A  reliable  method  is  that  known  as  the  copper-zinc  couple 
process,  by  which  all  the  oxidized  nitrogen  in  nitrates  and 
nitrites  is  reduced  to  ammonia  by  a  wet  copper-zinc  couple.  The 
ammonia  thus  obtained  can  be  distilled  over  and  estimated  in 
the  manner  described  in  Wanklyn's  process.  The  process  is  not 
suited  to  the  estimation  of  exceptionally  large  quantities  of 
nitrates,  but  it  is  very  accurate  up  to  i  part  of  N  as  nitrates  and 
nitrites  per  100,000,  and  is  therefore  applicable  to  the  very  large 
majority  of  waters  which  are  examined  as  to  their  fitness  for 
drinking  purposes. 

The  Process. 

1.  A  wet  copper-zinc  couple  is  prepared  by  taking  a  clean  and 
bright  piece  of  thin,  well-crumpled  zinc  foil,  and  well  cleansing 
this  with  dilute  sulphuric  acid.  Then  the  zinc  foil,  which  should 
measure  about  g  square  inches,  is  covered  with  a  saturated  solu- 
tion of  copper  sulphate,  and  very  quickly  the  surface  of  the  zinc 
loses  its  bright  appearance  and  becomes  covered  with  a  black 
adherent  coating  of  metallic  copper.  As  soon  as  this  coat  has 
thoroughly  formed — and  generally  about  three  minutes  will 
suffice — the  zinc  is  removed,  or  the  coating  becomes  pulverulent 
and  falls  away.  It  is  then  well  washed  with  distilled  ammonia- 
free  water.  The  wet  copper-zinc  couple  is  placed  in  a  thoroughly 
clean  8-ounce  glass-stoppered  bottle,  with  a  wide  mouth  in  order 
that  it  may  take  the  "  couple,"  and  no  c.c.  of  the  water  are 
poured  in  so  as  to  cover  the  "  couple,"  when  the  bottle  is  tightly 
stoppered  and  left  all  night  in  a  dark,  warm  place  (about  20"  C  ) 

With  very  soft  water  a  trace  of  sodium  chloride  should  be 
added  (about  o-i  gramme);  and  with  very  hard  waters  a  small 
quantity  of  pure  oxalic  acid,  to  precipitate  lime. 

2.  On  the  following  morning  10  c.c.  of  the  water  should  be 
removed  and  tested  for  nitrous  acid  by  Ilosvay's  test ;  the  absence 
of  this  acid  proves  the  completion  of  the  reducing  process,  and 
its  presence  demands  that  the  reaction  should  be  given  more  time 
in  which  to  complete  itself. 

3.  In  the  absence  of  nitrites  the  remainder  of  the  water 
(100  c.c.)  is  decanted  into  a  boiling-flask,  the  bottle  is  well 
washed  out  with  ammonia-free  distilled  water,  the  washings 

7 


98  LABORATORY   WORK 

being  also  added  to  the  flask,  and  then  about  400  c.c.  of  ammonia- 
free  water  are  added. 

4.  The  water  is  next  distilled  until  all  the  ammonia  present 
has  come  over.  This  is  then  Nesslerized  as  in  Wanklyn's 
method,  and  the  nitrogen  present  is  calculated  from  the  ammonia 
thus : 

The  molecular  weight  of  ammonia  being  17,  and  the  atomic 
weight  of  N  14;  N  =  yi  of  the  ammonia  estimated. 

Of  course,  the  amount  of  free  ammonia  originall}-  present  in 
100  c.c.  of  the  water  (and  which  has  already  been  estimated  by 
\Vankl3-n's  method)  must  be  deducted  from  the  total  ammonia 
produced  by  this  process. 

Example. — The  water  furnishes  0-25  milligramme  of  ammonia, 
and  since  all  of  this  must  have  been  yielded  by  100  c.c.  of  sample, 
0'25  part  per  100,000  is  present. 

But  by  Wanklyn's  method  the  water  showed  o-oo8  part  per 
100,000  of  free  and  saline  ammonia  as  originally  present. 

After  deducting  this  amount,  there  is  (o'25- 0'008= )  0*242 
part  of  ammonia  due  to  nitrates  and  nitrites  in  100,000  parts 
of  the  water  sample. 

The  results  are  expressed  in  terms  of  "  nitrogen  as  nitrates," 
or  as  "  nitrogen  as  nitrates  and  nitrites  "  in  those  cases  where 
nitrites  are  also  present.  Nitrogen  has  been  seen  to  form  \i  of 
ammonia,  therefore  there  are  |i  of  0*242  =  O'lgg  of  "  nitrogen 
as  nitrates,"  or  of  "  nitrogen  as  nitrates  and  nitrites,"  as  the  case 
may  be,  in  100,000  parts  of  water. 

If  in  those  cases  where  nitrates  co-exist  with  nitrites  it  should 
be  desired  to  express  the  nitrogen  of  the  nitrates  alone,  the 
nitrogen  yielded  by  nitrites  may  be  deducted.  Assuming  that 
the  water  has  been  found  by  the  Ilosvay  colorimetric  method  to 
contain  nitrogen  as  nitrous  acid  to  the  extent  of  0-029  P^-rt  per 
100,000,  then  0'i99-0"029  =  0"i7  is  the  amount  furnished  by 
nitrates  alone  in  100,000  parts. 

The  ammonia  thus  furnished  is  generally  in  considerable 
quantities,  and  the  colour  in  the  first  one  or  two  Nessler  glasses 
of  distillate  cannot  on  this  account  be  directly  matched  by  the 
chloride  of  ammonium  solution;  it  can  best  be  estimated  by 
mixing  the  distillate  collected  in  five  Nessler  glasses,  adding 
10  c.c.  of  Nessler  reagent,  and  then  matching  the  colour  in  an 
aliquot  part,  as  previously  recommended  (see  Wanklyn's  Method), 
and  then  calculating. 


OXIDIZED    NITROGEN    (NITRATES    AND    NITRITES)  99 

The  phenol-sulphonic  acid  colorimetrie  method  of  estimating 
nitrates  is  not  quite  so  exact  as  the  copper-zinc  couple  process, 
but  the  results  can  be  very  much  more  rapidly  arrived  at.  The 
lesser  delicacy  of  the  process  results  only  in  a  very  slight  error  of 
under-estimation,  which  docs  not  affect  one's  judgment  upon  the 
water. 

The  Special  Reagents  required  are : 

1.  Phenol-sulphonic  acid,  made  by  mixing  6  grammes  of  pure  phenol, 
3  c.c.  of  distilled  water,  and  37  c.c.  of  pure  sulphuric  acid.  Digest  for 
several  hours  at  82°  C.     Preserve  in  a  tightly  stoppered  bottle. 

2.  A  standard  solution  of  potassium  nitrate  (o-72i  gramme  to  the  litre), 
each  c.c.  of  which  contains  o-i  milligramme  of  nitrogen.  Dilute  tenfold, 
so  that  each  c.c  — o-oi. 

The  Process. 

1.  Ten  c.c.  of  the  water  sample  and  10  c.c.  of  the  standard 
nitrate  solution  are  each  placed  in  clean  platinum  dishes  and 
almost  evaporated  to  dryness. 

2.  Three  c.c.  of  the  phenol-sulphonic  acid  are  then  run  into 
the  dishes,  which  are  subsequently  placed  on  the  water-bath  for 
about  five  minutes. 

3.  The  contents  of  the  two  dishes  are  poured  into  two  separate 
Nessler  glasses,  and  the  dishes  are  carefully  washed  out  with 
25  per  cent,  ammonia  solution.  The  washings  of  each  dish  are 
added  to  the  Nessler  glass  which  originally  received  its  contents, 
and  then  more  25  per  cent,  ammonia  solution  is  cautiously  added 
to  each  glass  until  a  yellow  colour  remains. 

4.  The  contents  of  the  glasses  are  then  filtered  (if  necessary), 
and  made  up  to  50  c.c.  with  distilled  water.  The  Nessler  glass 
containing  the  standard  solution  assumes  a  distinct  yellow  colour 
(due  to  the  formation  of  potassium  nitrophenol-sulphonate) ,  and 
the  contents  of  the  other  Nessler  glass  are  also  coloured,  more  or 
less,  in  proportion  to  the  amount  of  nitrate  in  the  10  c.c.  of  water 
sample. 

By  transferring  measured  quantities  from  the  deeper  coloured 
liquid  (which  will  almost  always  be  that  containing  the  potassium 
nitrate  standard  solution)  into  other  Nessler  glasses,  which  are 
again  filled  up  with  distilled  water  to  their  marks,  a  match  is 
obtained;  thus  it  is  learnt  how  much  of  the  deeper  coloured  liquid 
is  required,  when  diluted  to  the  50-c.c.  mark  with  distilled  water 
to  match  the  tint  in  the  cylinder  with  the  less  colour;  or  the 
darker  solution  may  be  poured  into  a  measuring  glass  and  sue- 


100  LABORATORY   WORK 

cessive  additions  of  water  made  until  50  c.c.  poured  into  a  Nessler 
glass  is  found  to  effect  the  match. 

Suppose  that  5  c.c.  of  the  50  c.c.  of  the  darker  coloured 
(standard)  liquid  effect  a  match.  Then,  since  the  colour  in  the 
whole  of  the  standard  liquid  represents  10  c.c.  of  the  standard 
solution  of  nitrate  of  potassium,  the  colour  created  by  nitrates 
in  the  5  c.c.  =  (J\j  or  y\j  of  the  10  c.c.)  i  c.c.  of  the  standard 
solution. 

But  I  c.c.  of  the  standard  solution  contains  o-oi  milligramme 
of  nitrogen  as  nitrate;  therefore  there  is  o-oi  milligramme  of  such 
nitrogen  in  10  c.c.  (10,000  milligrammes)  of  water,  or  o"i  milli- 
gramme in  100,000  milligrammes  of  water,  or  0"i  part  per  100,000. 

If  the  sample  is  darker  than  the  standard,  then  measured 
quantities  of  the  sample  must  be  removed  and  made  up  to 
50  c.c.  with  distilled  water  until  a  match  is  obtained — e.g.,  sup- 
posing 25  c.c.  suffice  for  the  match,  then  the  sample  cylinder 
contains  twice  as  much  oxidized  N  as  the  standard  cylinder ;  and 
therefore  the  10  c.c.  of  original  water  contained  0"2  milligramme 
of  N  as  nitrates;  or  2  parts  per  100,000. 

Nitrites  slightly  add  to  the  colour  formed  in  this  process,  and 
chlorides  interfere  with  the  delicacy  of  the  estimation  by  furnish- 
ing lower  results.  If  chlorides  exceed  5  parts  chlorine  per 
100,000  in  the  original  water,  a  trace  of  pure  sodium  chloride 
should  be  added  to  the  standard  solution  of  nitrate  of  potassium. 

Conclusions  to  he  Drawn  from  the  Amount  Estimated. — The 
significance  of  the  presence  of  nitrites  and  nitrates  has  already 
been  discussed;  and  it  has  been  seen  that  high  nitrate  indicates 
previous  pollution,  either  distant  and  old,  or  near  and  recent. 
When  the  "  nitrogen  in  nitrates  "  exceeds  0"i  part  per  100,000, 
suspicion  is  certainly  justified  in  those  cases  where  the  strata 
may  be  excluded  as  the  source  from  which  the  water  may  have 
derived  such  nitrogen;  but  where  such  a  source  cannot  be  ex- 
cluded, an  amount  exceeding  0*5  would  be  regarded  as  suspicious, 
(or  it  is  exceptional  that  more  is  derived  from  entirely  harmless 
sources.  More  than  O'l  part  per  100,000  in  rain  or  upland 
surface  water  is  therefore  significant  of  animal  contamination. 
No  hard  limits,  however,  can  be  accepted  for  all  waters,  and  the 
amount  of  oxidized  nitrogen  must  be  considered  in  conjunction 
with  the  results  of  the  other  processes  that  help  to  furnish  evi- 
dence of  contamination. 


CHAPTER  XIII 

THE  GASES  IN  WATER 

It  is  the  aeration  of  water  which  furnishes  its  pleasant  taste  and 
sparkhng  appearance.  The  degree  of  aeration — as  has  been 
already  pointed  out— affords  no  evidence  of  the  water's  purity 
or  impurity,  since  the  foul  water  of  a  shallow  polluted  well  is 
frequently  markedly  aerated,  whereas  the  pure  water  collected 
from  great  depths  is  sometimes  poorly  so. 

Rain  water,  when  thoroughly  aerated,  contains  about  2073  c.c. 
of  gases  per  litre — i.e.,  nitrogen  i3"o8,  oxygen  6-37,  and  carbonic 
acid  I "28  c.c. 

In  addition  to  the  innocuous  gases  upon  which  the  aeration 
of  a  pure  water  depends — i.e.,  nitrogen,  oxygen,  and  carbonic 
acid— it  is  obvious  that  water  may  take  up  noxious  gases,  or  those 
which,  as  they  are  generally  the  products  of  organic  decomposi- 
tion, may  indicate  danger  (such  as  sulphuretted  hydrogen, 
ammonia,  marsh  gas  (CH4),  etc.). 

To  ascertain  whether  free  carbonic  acid  exists  in  the  presence 
of  bicarbonates,  a  solution  may  be  used  of  i  part  rosolic  acid 
in  500  parts  of  80  per  cent,  alcohol  (to  which  baryta  water  has 
been  added  until  it  begins  to  acquire  a  red  tint);  when  |  c.c. 
of  this  is  added  to  50  c.c.  of  water,  no  change  takes  place  if  free 
CO2  is  present,  but  a  distinct  reddening  occurs  in  the  absence  of 
free  COg. 

The  Lunge-Triliich  method  of  estimating  the  free  carbonic  acid 
is  very  easy  and  accurate. 

When  NajCOg  is  added  to  water  containing  free  COo,  sodium 
bicarbonate  is  formed  (Na2C03  +  C02  +  H20=  2NaHC03),  and 
when  all  the  free  CO2  is  combined  the  water  reacts  alkaline  to 
phenolphthalein.  The  amount  of  Na^COg  used  may  therefore  be 
made  to  indicate  the  amount  of  CO2  present. 

One  hundred  c.c.  of  the  sample  are  mixed  with  a  few  drops  of 


102  LABORATORY   WORK 

a  neutral  alcoholic  solution  of  phenolphthalein  and  titrated  in 
a  narrow  glass  cylinder  with  a  ^^f  solution  of  sodium  carbonate, 
until  a  faint,  but  permanent,  red  tint  appears.  This  gives  the 
amount  of  free  CO2. 

Example. — 2"2  c.c.  of  ^  NagCOg  were  required  to  neutralize 
the  free  CO2  in  100  c.c.  of  water. 

One  c.c.  of  ~y  Na^COg  contains  (  i;'^""  )  o"00265  gramme  of 
Na-^COg. 

But  106  parts  of  Xa^CO^  neutralize  44  parts  of  CO,. 

.•.  One  c.c.  of  -.^^  NaXOg^/j/.v  of  0"00265  =  0001  gramme  of 
CO.. 

.•.  2'2  C.C.  of  ttV  Na2C0j=  2'2  X  o'OOi  gramme  CO^  o"0022 
gramme  of  002- 

.•.  0  0022  gramme  COo  in  100  c.c.  water,  or  2'2  parts  per 
100,000. 

CO.  as  Carbonate  and  Bicarbonate  (Thorpe's  Method) : 

1.  Take  100  c.c.  of  water  in  a  flask  and  add  a  drop  or  two  of 
phenolphthalein. 

2.  Add  standard  oxalic  acid  solution  (2"863  grammes  of  pure 
recr3'stallized  oxalic  acid  to  the  litre  of  distilled  water,  i  c.c. 
of  which  equals  i  milligramme  of  COg)  until  the  phenolphthalein 
is  decolorized,  carefulh^  noting  the  amount  of  solution  used. 
This  will  indicate  the  CO2  present  as  carbonate. 

3.  Next  boil  the  water  for  about  ten  minutes,  and  then  note 
the  amount  of  standard  acid  required  to  decolorize. 

When  the  acid  is  first  added  to  the  water  the  carbonates  are 
converted  into  bicarbonates,  and  when  this  conversion  is  com 
plete  the  phenolphthalein  is  decolorized. 

When  the  water  is  boiled  CO2  is  driven  off,  and  the  converted 
bicarbonates  and  the  original  bicarbonates  are  reduced  to  car- 
bonates. The  second  titration  will  furnish  the  amount  of  CO2 
remaining  after  boiling.  Twice  this  quantit}/  will  represent  the 
total  CO2  as  bicarbonates  prior  to  boiling,  and  this  amount  less 
the  original  CO2  in  carbonates  will  furnish  the  amount  of  CO2 
as  bicarbonates  originally  in  the  water. 

Example. — One   hundred   c.c.    of  water  required  2 "5    c.c.    of 
oxalic  acid=  2*5  milligrammes  of  CO2  as  carbonates,  or  2*5  parts, 
per  100,000. 

After  boiling,  3-5  c.c.  of  oxalic  acid  were  required.  The  total 
CO2  as  bicarbonates  is  therefore  7  milligrammes.     Deduct  the 


THE    GASES    IN   WATER  IO3 

2-5,  and  the  amount  in  the  original  water  was  4-5   i)arts  per 
100,000. 

Sulphuretted  hydrogen  frequently  gains  access  to  water 
through  organic  substances  undergoing  putrefaction,  or  in- 
directly from  industrial  waste  matters.  It  may  be  derived  from 
mineral  sulphides,  or  from  reduction  of  mineral  sulphates  in 
soil,  etc.  (which  reduction  is  frequently  effected  by  organic  matter 
and  hving  organisms,  such  as  Beggiatoa  alha). 

Good  examples  of  waters  charged  with  sulphuretted  hydrogen 
from  harmless  sources  are  to  be  found  notably  at  Harrogate  and 
Aix-la-Chapelle.  The  waters  from  some  clays  have  a  distinct 
amount  of  sulphuretted  hydrogen,  derived  from  the  tiny  particles 
of  iron  pyrites  which  enter  into  the  composition  of  the  clay. 

When  sulphuretted  hydrogen,  ammonium  sulphide,  or  the 
constituents  of  coal  gas  are  present,  the  water  will  generally  be 
condemned,  as  either  unsuitable  for  a  domestic  supply  or  as 
polluted. 

If  HgS  is  in  considerable  amount,  the  addition  of  a  solution  of 
acetate  of  lead  produces  a  brownish  coloration 

(Pb(C2H30,)2  +  HgS^  PbS  +  2C2H4O2). 

The  gas  may  be  estimated  while  in  the  water  in  the  following 
manner : 

Take  a  large  flask  and  add  10  c.c.  of  centinormal  iodine  solu- 
tion; then  run  in  a  measured  quantity  of  the  water  until  the 
yellow  colour  of  the  free  iodine  disappears  (I2+ H2S=2HI  + S); 
then  add  5  c.c.  of  starch  solution,  and  run  in  more  of  the 
iodine  solution  cautiously  until  a  blue  colour  just  begins  to 
show  itself.  Of  the  iodine  solution  used  each  c.c.  will  have 
decomposed  0-17  milligramme  of  HgS,  and  therefore  the  total 
will  represent  17  milligrammes  of  HgS.  The  slight  excess  of 
iodine  required  to  produce  the  blue  colour  is  trivial,  but  it  may 
be  estimated  and  deducted  by  titrating  back  with  sodium  thio- 
sulphate. 

Centinormal  iodine  (1-26  grammes  iodine  per  litre)  is  pre- 
pared as  follows : 

Iodine  is  never  quite  pure,  and  is  very  volatile.  Dissolve  therefore 
about  I -3  grammes  in  a  solution  of  2  grammes  of  potassium  iodide  in 
50  c.c.  of  water,  and  dilute  to  a  litre;  then  further  dilute  until  10  c.c. 
of  the  solution,  coloured  blue  with  a  few  drops  of  starch  solution,  are 
decolorized  by  exactly  10  c.c.  of  centinormal  sodium  thiosulphate  (2-464 
grammes  to  a  litre) .     The  solution  should  be  kept  in  the  dark. 


104  LABORATORY    WORK 

Evidence  of  odorous  gases  may  be  obtained  by  heating  the 
water  to  60°  C,  in  the  manner  already  described  in  reference  to 
"odour."  A  few  drops  of  a  solution  of  the  nitro-prusside  of 
sodium  \vill  distinguish  between  sulphuretted  hydrogen  and 
ammonium  sulphide,  for  that  solution  furnishes  a  violet-purple 
colour  with  ammonium  sulphide,  but  no  change  results  if  sul- 
phuretted hydrogen  alone  be  present. 

Some  waters  issuing  as  springs  in  the  vicinity  of  volcanoes 
are  charged  with  sulphurous  acid. 

The  Estimation  of  the  Oxygen  Dissolved  in  Water. 

The  estimation  of  oxygen  is  of  some  importance,  for  it  gives 
a  clue  to  the  self-purifying  power  of  the  water,  and  it  is  rapidly 
diminished  in  oxidizing  the  C  and  N  of  any  putrescent  organic 
matter  present. 

Dr.  Thresh  has  devised  a  satisfactory  process  for  this  estima- 
tion, one  that  is  quickly  performed  and  easy  of  execution. 

When  dilute  sulphuric  acid  and  the  iodide  of  potassium  are 
added  to  water  containing  nitrite,  iodine  is  liberated,  the  amount 
varying  with  the  length  of  time  during  which  the  mixture  is 
exposed  to  the  air.  If  air  be  carefully  excluded  there  is  no  in- 
crease in  the  amount  of  iodine  set  free  after  the  first  few  minutes. 
We  have  only,  therefore,  to  add  to  a  known  quantity  of  the 
water  a  definite  amount  of  sodium  nitrite,  together  with  excess 
of  potassium  iodide  and  acid  (avoiding  access  of  air),  and  then 
to  determine  volumetrically  the  amount  of  iodine  liberated. 
After  certain  deductions  the  remainder  represents  the  dissolved 
oxygen  present  in  the  water. 

The  following  are  the  reagents  required : 

1.  Solution  of  sodium  nitrite  and  potassium  iodide: 

Sodium  nitrite  . .        0-5  gramme. 

Potassium  iodide      . .      20-0  grammes. 
Distilled  water  .  .      100  c.c. 

2.  Dilute  sulphuric  acid,  i  in  4. 

3.  A  clear  or  fresh  solution  of  starch. 

4.  A  volumetric  solution  of  sodium  thiosulphate:  Pure  crystals  of 
thiosulphate,  7-75  grammes;  distilled  water,  to  i  litre.  One  c.c.  corre- 
sponds to  0-25  milligramme  of  oxygen.     Keep  in  small  bottles  in  the  dark. 

The  apparatus  is  used  in  the  following  manner : 
The  bottle  A  being  clean  and  dry,   the  perforated  bung  is 
inserted,  the  burette  charged,  and  the  tube  B  fixed  in  its  place. 


THE    GASES    IN    WATER  IO5 

E  is  connected  with  the  gas  supply.  The  tube  D  is  filled  to  the 
level  of  the  stopper  with  the  water  to  be  examined,  then  i  c.c. 
of  the  solution  of  sodium  nitrite  and  potassium  iodide  and  i  c.c. 
of  the  dilute  acid  are  added,  and  the  stopper  instantly  fixed  in 
its  place,  displacing  a  httle  of  the  water  and  including  no  air. 
If  the  pipette  be  held  in  a  vertical  position,  both  the  saline 
solution  and  the  acid,  being  much  denser  than  the  water,  flow 


FIG.    15. APPARATUS    FOR    THRESH  S    PROCESS. 


in  a  sharply  defined  column  to  the  lower  part  of  the  tube,  so 
that  an  infinitesimally  small  quantity  (if  any)  is  lost  in  the 
water  which  overflows  when  the  stopper  is  inserted.  The  tube 
is  next  turned  upside  down  for  a  few  seconds  for  uniform  ad- 
mixture to  take  place,  and  then  the  nozzle  is  pushed  through 
the  bung  of  the  bottle,  and  the  whole  allowed  to  remain  at  rest 
for  fifteen  minutes  to  enable  the  reaction  to  become  complete. 
A  rapid  current  of  coal  gas  is  now  passed  through  the  bottle  A 


I06  LABORATORY    WORK 

until  all  the  air  is  displaced,  and  the  gas  lighted  at  G  burns  with 
a  full  luminous  flame.  The  flame  is  then  extinguished,  the 
stopper  of  D  removed,  and  the  cork  G  rapidly  inserted  in  its 
stead.  On  turning  the  stopcock  the  water  flows  from  D  into 
the  bottle  A,  which  now  contains  no  oxygen.  The  stopcock  is 
turned  off,  the  cork  G  removed,  and  the  supply  of  gas  regulated 
so  that  a  small  flame  only  is  produced  when  this  gas  is  ignited 
at  G.  The  thiosulphate  is  now  run  in  slowly  from  the  burette 
C  until  the  colour  of  the  iodine  is  nearly  discharged.  A  little 
solution  of  starch  is  then  poured  into  D,  and  about  i  c.c.  allowed 
to  flow  into  the  bottle  by  turning  the  stopcock.  The  titration 
with  thiosulphate  is  then  completed.  After  the  discharge  of  the 
blue  colour,  the  latter  returns  faintly  in  the  course  of  a  few 
seconds,  due  to  the  oxvgen  dissolved  in  the  volumetric  solution; 
therefore,  after  about  two  minutes  o-i  c.c.  of  thiosulphate  must 
be  added  to  effect  the  final  discharge.  The  total  amount  of 
thiosulphate  solution  used  must  now  be  noted.  This  will  repre- 
sent the  iodine  liberated  on  account  of — 

(a)  The  oxygen  dissolved  in  the  sample  used. 

(b)  The    chemical  interaction  between  the  KI.NaNOg  and 

H2SO4. 
(r)  The  oxygen  dissolved  in  the  reagents  added. 
(d)  Any  nitrous  acid  present  as  nitrite  in  the  sample  would 

liberate  a  little  more  iodine. 

To  find  the  value  of  (a),  it  is  obvious  that  the  value  of  (&),  (c) 
and  (d)  must  be  ascertained.  The  value  of  {b)  and  (c)  can  be 
most  readily  found  by  making  a  blank  experiment,  by  adding 
to  the  apparatus  2  c.c.  of  the  nitrite  iodide  solution,  3  c.c.  of 
acid,  3  c.c.  of  starch,  and  distilled  water  equal  to  twice  the 
volume  of  thiosulphate  used  in  the  analysis,  and  titrating  with 
thiosulphate  as  in  the  actual  experiment.  Half  the  thiosulphate 
solution  used  represents  the  amount  which  must  be  deducted 
on  account  of  (b)  and  (r). 

To  find  the  value  of  {d),  a  water  containing  nitrites  will  require 
the  amount  of  the  nitrous  acid  to  be  determined  if  the  utmost 
accuracy  is  required  (A  water  containing  i  part  HNOg  in  1,000,000 
will  effect  the  results  +0-17  milligramme  of  oxygen  per  htre; 
94  parts  of  the  acid  corresponding  to  16  of  oxygen).  Where 
nitrites  are  present  in  sufficient  quantity  to  interfere,  the  amount 
may  be  determined  by  any  of  the  ordinary  processes. 


THE    GASES    IN    WATER 


107 


Notes.— The  test  depends  on  the  liberation  of  iodine  anrl  nitric 
oxide  (NO),  by  the  interaction  of  sodium  nitrite,  potassium 
iodide,  and  sulphuric  acid  in  the  water,  and  the  NO  combines 
with  what  dissolved  oxygen  is  present  to  form  nitric  trioxide 
(N2O3).  This  N2O3  then  liberates  a  further  quantity  of  free 
iodine,  which  is  therefore  proportionate  to  the  amount  of  dis- 
solved oxygen  in  the  water.  The  total  iodine  is  then  determined 
by  sodium  thiosulphate  solution,  and  the  amount  furnished  by 
the  dissolved  oxygen  can  be  calculated.  The  various  chemical 
reactions  are  as  follows: 


(i)  2KI  +  2NaN02 
(2)  2HI  +  2HNO2  - 


h  2H2SO4  ==  K2SO4  +  Na2S04  +  2HNO2  +  2HI. 
I2  +  2NO  +  2H2O. 

(3)  2NO  + dissolved  0  in  water  =N203;  and  the  N2O3  in 
contact  with  hydriodic  acid  hberates  a  further  quantity  of 
iodine,  which  is  therefore  equivalent  to  the  oxygen  present : 

(4)  2HI  +  N2O3  =  2NO  + 12  +  H2O. 

The  sodium  thiosulphate  reacts  with  the  liberated  iodine  as 
follows : 

(5)  2Na2S203  +  l2  =  Na2S406  +  2NaI. 

Samples  should  always  be  drawn  from  the  water  in  a  quiescent 
condition,  and  every  precaution  must  be  taken  to  avoid  splashing 
or  further  aeration. 

A  few  of  the  results  got  by  Thresh  are  as  follows : 


Source  of  Water. 

i 

Amount  of 

Water 
employed. 

1 

Total  Thio- 
sulphate 
required. 

Thio- 
sulphate 
required 
by  the  Dis- 
solved 0  in 
the  Water. 

1 

1 

MiUi-       i 
grammes  O 
per  Litre. 

1.  Spring  water 

2.  Rain  water  .  . 

3.  Shallow-well  water .  . 

4.  Rain  water  .  . 

5.  Distilled  water  shaken  with 

air 

322-0 
322-0 
322-0 
322-0 

322-0 

12-35 
13-05 
11-35 
12-95 

16-00 

9-87 

10-55 

8-90 

10-45 
13-40 

7-66 
8-19 
6-91 

8-II 

i 

10-40 

Nitrites,  ferrous  iron,  sulphides,  and  a  large  quantity  of 
organic  matter  will  vitiate  the  estimation,  but  Rideal  has  pointed 
out  that  it  is  practicable  to  get  rid  of  the  interference  due  to 
nitrites,  organic  matter,  etc.,  by  oxidizing  with  permanganate 
in  acid  solution  out  of  contact  with  air. 


I08  LABORATORY   WORK 

The  process  gives  results  closety  approximating  to  those 
obtained  by  a  gasometric  process. 

A  simpler  method  for  the  estimation  of  dissolved  O  in  water 
is  that  of  Winkler : 


Winkler's  Method  for  the  Estimation  of  Dissolved  Oxygen  in 

Water. 

In  collecting  the  sample  of  water,  care  must  be  taken  to  avoid 
agitating  it  and  exposing  it  for  any  length  of  time  to  the  air. 

1.  A  portion  of  the  sample  is  transferred  with  the  above- 
mentioned  precautions  to  a  glass-stoppered  bottle  of  known 
capacity.  A  suitable  capacit}-  is  about  300  c.c,  and  the  bottle 
must  be  completely  filled. 

2.  One  c.c.  of  strong  manganous  chloride  solution  (40  grammes 
of  MnCUHgO  to  100  c.c.  of  distilled  water)  is  added,  followed  by 
2  c.c.  of  a  solution  containing  33  per  cent,  caustic  potash  and 
10  per  cent,  potassium  iodide. 

3.  The  bottle  is  stoppered  without  including  any  air-bubble, 
and  the  liquids  are  mixed  by  several  times  inverting  the  bottle. 
The  manganous  hydroxide  precipitate  which  forms  will  be  more 
or  less  discoloured  by  higher  hydroxide,  according  to  the  propor- 
tion of  oxygen  which  was  dissolved  in  the  water  sample. 

4.  As  the  oxidation  of  the  manganous  hydroxide  is  not 
immediate,  and  the  result  is  influenced  by  light,  the  bottle  is 
put  aside  in  a  dark  cupboard  for  fifteen  minutes;  2  to  3  c.c. 
of  pure  strong  hydrochloric  acid  are  then  added  by  means  of  a 
pipette  inserted  into  the  bottle,  so  that  the  acid  will  fall  upon  the 
precipitate,  when  the  precipitate  disappears  and  leaves  the  liquid 
coloured  with  dissolved  iodine,  which  is  proportionate  in  amount 
to  the  higher  hydroxide  formed,  and  therefore  to  the  dissolved 
oxygen  in  the  water. 

5.  Pour  the  contents  of  the  bottle  into  a  clean  beaker,  washing 
out  the  bottle  with  distilled  water  and  also  adding  the  washings 
to  the  beaker,  and  then  titrate  the  iodine  with  decinormal  sodium 
thiosulphate,  of  which  i  c.c.  is  equivalent  to  o-ooo8  gramme  of 
oxygen.  Starch  should  be  used  for  the  end  reaction,  as  recom- 
mended in  Tidy's  process. 

Example. — Capacity  of  bottle  (283  c.c.)  less  the  3  c.c.  of  solu- 
tion added  =280  c.c.  The  decinormal  sodium  thiosulphate 
required  in  the  test  was  2-8  c.c.  =  0"00224  gramme  of  oxygen. 


THE    GASES    IN    WATER  lOQ 

Therefore  there  is  0-00234  gramme  of  dissolved  oxygen  in  280  c.c. 
of  water=0"0008  gramme  of  oxygen  in  100  c.c.  of  water  = 
o-oo8  gramme  of  oxygen  in  1,000  c.c.  of  water,  or  8-0  milHgrammes 

per  Htre. 

Notes  on  the  Process.— Sometimes  the  amount  of  thiosulphate 
required  by  the  same  volume  of  fully  aerated  distilled  water  is 
determined,  and  the  percentage  of  dissolved  oxygen  in  the 
sample  is  compared  with  the  amount  of  thiosulphate  which  equal 
volumes  of  these  two  waters  require. 

The  manganous  chloride  must  be  free  from  iron,  and  all  the 
reagents  must  be  free  from  nitrites. 

The  process  must  be  done  rapidly.  Nitrites  liberate  iodine 
and  so  vitiate  the  result  by  increasing  it.  Much  organic  matter 
interferes  with  the  method,  for  it  absorbs  liberated  iodine,  and 
thus  diminishes  the  result. 

The  chemistry  of  the  process  is  explained  by  the  following 

equations : 

(i)  2Mna2  +  4NaOH  =  4NaCl  +  2Mn(OH)2. 

(2)  2Mn(OH)2  +  0  +  H20=2Mn(OH)3. 

(3)  2Mn(OH)3  +  6HCl=2MnCl3  +  6H20. 

(4)  2Mna3  +  2KI=2MnCl2  +  2KCl  +  l2. 

The  amount  of  dissolved  oxygen  in  a  water  is  influenced  by 
temperature,  being  less  in  summer  and  more  in  winter.  Ordinary 
tap  water  in  this  country  contains  between  6  and  7  c.c.  per  litre, 
or  about  i  part  by  weight  in  100,000.  Water  is  saturated  at 
5°  C,  10°  C,  15°  C,  and  20°  C.  respectively,  by  8-68  c.c,  777  c.c. 
6-96  c.c,  and  6-28  c.c  per  litre. 

When  nitrites  excaed  faint  traces  the  results  are  too  high  o^Adng 
to  the  reaction  between  the  nitrous  acid  and  hydriodic  acid;  the 
reaction  is  catalytic,  the  nitric  oxide  formed  absorbing  oxygen 
from  the  air  and  yielding  nitrous  acid,  which  in  turn  decom- 
poses a  further  quantity  of  hydriodic  acid.  This  effect  may  be 
prevented  by  carrying  out  the  method  in  the  usual  way,  and 
introducing  2  c.c.  of  potassium  acetate  solution  (1,000  grammes 
per  htre)  when  the  precipitate  has  dissolved  in  the  added  hydro- 
chloric acid.  The  acetate  solution  should  be  added  by  means 
of  a  pipette  reaching  to  the  bottom  of  the  bottle  (Hale  and 
Meha). 


CHAPTER  XIV 

COMPOSITION  OF  WATER  FROM  VARIOUS  SOURCES— 
THE  OPINION  ON  WATER  SAMPLES 

Waters  from  the  subsoil,  from  cultivated  surfaces  and  from 
rivers  are  especial!}^  liable  to  be  organically  polluted;  and  the 
character  of  the  deposit  from  which  the  water  is  collected  in- 
fluences its  composition  to  an  extent  which,  though  variable, 
may  be  approximately  defined. 

I.  Surface  Waters. — Those  waters  collected  from  the  hard  sur- 
faces of  the  practically  impervious  rocks,  which  support  httle 
animal  or  vegetable  life,  are  very  pure.  They  commonly  contain 
less  than  lo  parts  of  total  solids,  5  of  total  hardness,  i  of  chlorine, 
and  o-i  of  nitrogen  as  nitrates,  in  100,000  parts  of  water.  The 
mineral  solids  consist  mainly  of  sodium  carbonate  and  chloride, 
and  a  trace  only  of  lime  or  magnesia.  The  organic  matter,  which 
is  often  exclusively  of  vegetable  origin  (peat),  yields  practically 
no  free  ammonia;  but  the  organic  ammonia  figure  and  that  of  the 
oxygen  absorbed  by  organic  matter  may  be  high,  in  which  case 
the  water  is  often  highly  coloured  and  acid  in  reaction.  Such 
characters  are  presented  by  the  waters  collected  from  the  sur- 
faces of  the  igneous,  metamorphic  (quartz,  mica,  granite,  etc.), 
Cambrian,  Silurian  and  Devonian,  rocks. 

Waters  from  the  surface  of  the  non-calcareous  carboniferous 
rocks  (Yoredale  rocks,  millstone  grits  and  coal-measures)  are 
very  similar;  but  those  which  have  flowed  over  the  surfaces 
of  the  calcareous  carboniferous  rocks — the  mountain  limestone 
and  limestone  shales — differ  from  the  former  in  possessing  a 
moderate  degree  of  hardness,  higher  total  solids  and  a  neutral 
or  faintly  alkaline  reaction,  the  mineral  solids  consisting  chiefly 
of  sulphate  and  carbonate  of  calcium  and  magnesium. 

Surface  waters  from  the  lias,  new  red  sandstone,  magnesian 
limestone   and   oolite   vary   considerably'  in    their   composition. 


COMPOSITION    OF   WATER   FROM    VARIOUS    SOURCES      III 

The  total  solids  are  generally  between  lo  and  20  parts  per  100,000, 
the  total  hardness  between  10  and  15;  the  chlorine  is  below  2. 
and  the  nitrogen  as  nitrates  below  0-2  of  a  part  per  100,000. 

Clay  surface  waters  are,  as  a  rule,  opaque  from  a  variable 
quantity  of  suspended  matter,  but  generally  there  are  few  dis- 
solved solids,  and  the  water  is  fairly  soft.  They  vary  greatly, 
however,  in  their  composition. 

Waters  collected  from  cultivated  land  present  great  varia- 
tions in  composition;  the  total  hardness  may  range  from  5  to 
25  parts  per  100,000,  according  as  to  whether  the  soil  is  non- 
calcareous  or  calcareous. 

Alluvium  is  generally  a  mixture  of  sand,  clay  and  organic 
matter;  and  waters  from  such  a  source  mostly  contain  high 
mineral  sohds  (50  to  100  parts),  consisting  of  calcium  and 
magnesium  salts,  sodium  chloride,  iron,  and  silica. 

2.  Waters  from  a  Depth. — Those  collected  from  the  chalk  are 
generally  clear,  bright,  and  well  charged  with  carbonic  acid. 
The  total  sohds  are  generally  from  25  to  50  parts  per  100,000, 
and  the  total  hardness  from  15  to  30  parts;  the  hardness  is 
mostly  temporary,  and  calcium  carbonate  may  vary  from  10  to 
30  parts.  The  chlorine  is  commonly  from  2  to  4,  but  it  may 
reach  a  higher  figure  in  some  pure  chalk  waters.  The  nitrogen 
as  nitrates  is  generally  below  0-5  part  per  100,000,  and  is  com- 
monly about  0-2.  Sulphates  are  present  in  small  quantity,  and 
there  is  often  a  trace  of  phosphates  and  of  iron.  Although  the  car- 
bonic acid  present  may  be  sufficient  to  turn  blue  litmus  red,  when 
this  gas  is  driven  off  by  heat  an  alkaline  action  is  invariably 
obtained. 

Some  waters  from  the  chalk  are  very  soft,  and  contain  sodium 
carbonate.  They  are  only  found  where  the  chalk  lies  buried 
beneath  a  thick  mass  of  London  clay  (Thresh). 

Waters  from  the  oolite  present  characters  very  similar  to  those 
from  the  chalk. 

Those  derived  from  limestone  and  magnesium  limestone  for- 
mations only  differ  from  the  chalk  waters  in  generally  containing 
more  total  solids,  far  more  calcium  or  magnesium  sulphate 
(which  may  reach  nearly  20  parts  per  100,000),  and  less  calcium 
or  magnesium  carbonate;  and  by  consequence  the  hardness  is 
generally  higher  and  in  a  greater  proportion  "  permanent." 

In  dolomite  districts  the  mineral  solids  contain  much  mag- 
nesium carbonate  and  sulphate,  and  a  large  proportion  of  the 


112  LABORATORY   WORK 

total  hardness  is"  permanent,"  dolomite  being  a  double  carbonate 
of  lime  and  magnesia. 

The  greensands  are  porous  strata  containing  a  reducing  salt 
of  iron,  which,  by  reducing  oxidized  nitrogen  to  ammonia,  often 
furnishes  to  the  water  a  very  high  figure  of  free  and  saline 
ammonia.  The  total  soHds  vary  considerably,  but  they  some- 
times approach  loo  parts  per  100,000  where  the  water  is  col- 
lected at  great  depths  in  greensand  underlying  the  chalk; 
the  chlorine  may  reach  a  figure  of  from  4  to  15;  the  total  hard- 
ness (much  of  which  is  "  permanent  ")  is  very  variable — from 
a  low  to  a  high  figure;  and  the  nitrogen  as  nitrates  is  generally 
from  about  0-3  to  o-6  part  per  100,000. 

Where  the  lower  greensand  is  exposed  it  is  very  porous,  and 
many  of  the  waters  yielded  from  it  contain  but  little  lime  and 
hardness.  The  total  solids  are  often  small  in  amount,  and  the 
chlorine  and  sahne  constituents  (including  ammonia)  may  be  low. 
A  marked  amount  of  nitrate  is  often  present,  and  not  infrequently 
a  considerable  quantity  of  iron  is  found  in  solution.  Such  waters 
differ  materially  from  those  obtained  from  the  covered  beds; 
the  latter  often  containing  large  amounts  of  saline  matter  (chiefly 
alkaline  chlorides,  sulphates,  and  carbonates).  This  difference 
in  the  composition  of  the  waters  from  exposed  greensand  and 
those  from  covered  beds  is  probably  accounted  for  by  the  ex- 
planation that  the  soluble  constituents  in  the  very  porous 
exposed  part  of  the  bed  have  been  largely  washed  out  by  the 
rapidly  percolating  waters. 

Waters  from  red  sandstone  strata  vary  considerably  in  their 
composition,  according  as  the  deposit  is  pure  or  impure,  soft  or 
hard.  The  total  solids  and  total  hardness  are  both  sometimes 
high,  and  the  former  may  reach  100  parts  per  100,000;  the  latter 
is  mainly  of  a  permanent  nature,  but  the  water  may  sometimes 
be  soft  and  possess  a  total  hardness  figure  not  exceeding  10  parts 
per  100,000.  The  chlorine  may  vary  from  3  to  6;  and  traces 
of  phosphates  are  always  to  be  detected  in  the  mineral  solids, 
which  consist  in  the  main  of  sodium  chloride,  carbonate  and 
sulphate,  calcium  and  magnesium  carbonates  and  sulphates, 
and  a  trace  of  iron. 

Waters  from  selenitic  deposits  are  sometimes  objectionable,  on 
account  of  the  large  proportion  of  calcium  sulphate  (10  to  30,  or 
more,  parts  per  100,000)  which  is  taken  up  from  this  deposit, 
which  itself  consists  of  calcium  sulphate  in  clear  crystals. 


THE   OPINION   ON   WATER   SAMPLES  113 

Waters  collected  from  loose  sands  are  of  variable  composition. 
Some  are  soft,  with  total  solids  of  from  only  6  to  12  parts  per 
100,000,  and  others  are  rather  hard  (permanent)  with  mineral 
solids  amounting  to  even  100  parts.  The  chlorine  figure  is 
generally  rather  high,  and  may  reach  to  a  very  high  figure  in 
some  cases.  The  mineral  solids  consist  of  sodium  chloride, 
carbonate  and  sulphate,  calcium  and  magnesium  salts,  and  traces 
of  iron  and  silica.  Those  from  gravel  are  generally  soft,  but 
some  are  liard,  with  rather  high  total  solids.  Waters  of  the 
latter  class  coming  from  a  depth  have  often  very  high  mineral 
sohds  (often  consisting  largely  of  calcium  and  magnesium  sul- 
phate). There  is,  as  a  rule,  some  opacity,  and  the  physical 
characters  generally  are  not  favourable  to  the  water.  The  hard- 
ness, which  is  almost  entirely  "  permanent,"  is  often  over  20, 
and  the  mineral  solids  may  in  some  cases  reach  a  high  figure. 

Deep  wells,  when  protected  from  surface  drainage  and  ground 
water  in  their  upper  parts,  are  but  rarely  polluted,  even  when 
situated  in  the  centres  of  towns.  But  it  does  occasionally  happen 
that  Hquid  soakage  from  sewers  or  cesspools  finds  its  way  into 
fissures  in  chalk  or  sandstone,  which  conduct  it  to  the  water  of 
the  well,  maybe  from  a  considerable  distance. 

The  Opinion  on  Water  Samples. 

If  the  analysis  does  not  justify  suspicion,  and  local  circum- 
stances do  not  favour  any  form  of  dangerous  contamination, 
then,  and  then  only,  may  the  water  be  judged  safe  for  drinking 
purposes. 

Either  a  chemical  analysis  or  a  bacterioscopic  examination 
may  alone  suffice  to  demonstrate  the  fitness  of  a  water  for  drink- 
ing purposes,  but  the  two  processes  are  complementary  to  each 
other,  and  it  is  essential  in  many  cases  that  they  should  both 
be  performed.  Neither  is  infallible;  the  value  of  one  is  often 
greatly  enhanced  by  the  other;  and  the  value  of  both  depends 
upon  the  correct  interpretation  of  results. 

Between  an  undoubtedly  bad  water  and  an  undoubtedly  good 
water  there  are  waters  regarding  which  no  opinion  ought  to 
be  advanced  unless  advantage  is  taken  of  a  careful  local  inspec- 
tion to  detect  any  possible  source  of  pollution  and  both  a  bacterio- 
logical examination  and  a  chemical  analysis  are  performed. 

It  is  true  that  so  small  an  amount  of  organic  matter  as  would 
not  call  for  condemnation  of  the  water  may  yet  contain  the 


114  LABORATORY    WORK 

specific  germs  of  disease;  but  chemical  analj'Sis  will  generally 
reveal  impurity  and  risk.  As  specific  germs  always  gain  access 
to  the  water  in  the  media  of  dirt  and  animal  matter,  it  is  rare 
that. the  chemical  examination  fails  to  indicate  the  danger;  but 
whenever  there  is  any  reason  to  suppose  that  a  water-supply  is 
infected  with  typhoid  or  cholera  organisms,  a  bacterioscopic 
examination  becomes  imperative.  Indeed,  the  circumstances 
which  call  for  the  analysis  of  a  particular  sample  should  always 
weigh  with  one  in  fixing  the  standard  of  purity  which  will  justify 
the  opinion  that  the  water  may  be  consumed  with  safet3^ 

The  detection  of  a  very  fine  amount  of  organic  contamination 
in  shallow  wells  may  often  be  made  by  collecting  samples  from 
several  wells  in  the  near  neighbourhood  of  each  other,  and  taking 
the  purest  of  these  waters  as  a  standard. 

In  judging  of  the  purity  of  water  from  a  river  or  small  stream, 
it  will  sometimes  be  advantageous  to  make  an  analysis  of  tribu- 
tary streams  emptying  into  it. 

Water  from  different  sources  (peaty  and  non-peaty  surface 
waters,  waters  from  shallow  and  deep  sources)  have  their  own 
characteristics,  and  the  various  quantitative  estimations  must  be 
interpreted  accordingly.  It  is  impracticable  to  lay  down  hard- 
and-fast  standards  of  purity  (either  chemical  or  bacteriological) 
to  which  all  waters  must  conform,  irrespective  of  their  source. 

In  expressing  an  opinion  upon  the  analytical  results,  it  is  very 
desirable  to  give  expression  to  the  necessary  limitations  of  the 
examination.  Thus,  it  will  be  better  to  say,  "  The  chemical 
analysis  of  the  sample  shows  no  evidence  of  harmful  organic 
pollution,"  than  to  employ  such  a  statement  as,  "  There  is  no 
harmful  organic  pollution  in  this  water."  In  order  to  commit 
oneself  to  a  statement  which  would  imply  that  the  water-supply 
is  a  constantly  pure  one,  it  will  often  be  necessary  to  examine 
several  samples  at  different  seasons  of  the  year  and  under  dif- 
ferent conditions  as  to  rainfall. 

Water  Standards. — It  would  often  be  of  assistance  to  analysts 
if  they  carefully  constructed  "  water  standards  "  in  their  dis- 
tricts. Such  would  be  prepared  from  the  purest  water  in  each 
locality,  and  they  would  form  a  reliable  means  of  detecting  the 
smallest  amount  of  impurity  which  gains  access  to  any  particular 
supply.  For  instance,  a  water  sample  may  well  contain  0"004 
part  per  100,000  of  free  and  saline  ammonia  and  2  parts  per 
100,000  of  chlorine,  without  any  suspicion  of  danger  being  war- 
ranted; but  if  the  average  of  the  pure  water  of  the  particular 


THE    OPINION    ON    WATER    SAMPLES 


115 


locality  is  0'002  part  of  free  and  saline  ammonia  and  i'5  parts 
of  chlorine,  then  the  excess  found  would  furnish  important 
evidence  of  animal  pollution. 

In  some  of  the  American  States,  Massachusetts  notably,  the 
normal  distribution  of  chlorine  has  been  mapped  out.  This  has 
been  done  by  estimating  the  amount  of  chlorine  in  the  unpol- 
luted waters  of  the  district  at  a  large  number  of  points,  and  thus 
ascertaining  the  normal  distribution  of  chlorine  in  every  par- 
ticular locality.  When  lines  are  drawn  upon  the  district  map 
which  join  together  the  localities  where  the  chlorine  figures  corre- 
spond, these  lines  are  known  as  "  isochlors."  The  plans  of  the 
"  isochlors"  are  valuable,  as  when  in  a  given  spot  an  amount 
of  chlorine  is  found  in  excess  of  the  figure  of  the  particular 
"  isochlor "  of  the  locality,  it  furnishes  material  evidence  of 
sewage  pollution. 

Chlorine  standards  are  of  the  most  value  when  they  relate 
to  surface  water,  in  which  the  small  clilorine  figure  remains  very 
uniform  indeed  in  the  absence  of  animal  pollution;  but  even  then 
they  often  fail  to  indicate  harmful  pollution.  The  superior  value 
of  the  "  free  and  saline  "  ammonia  figure  is  very  apparent  in  the 
following  results: 


' 

1 
A. 
Water. 

B. 

Sewage. 

0. 

Water+i^n  per 
cent,  of  Sewage. 

Parts  per  100,000. 

Parts  per  ioo,coo. 

Parts  per  100,000. 

Free  and  saline  ammonia 

0-0005 

6-2IOO 

0-0067 

Albuminoid  ammonia 

0-0035 

1-3200 

0-0048 

Oxygen  absorbed  in  2  hours 

at27°C. 

0-0300 

4-1430 

0-0341 

Total  solids 

30-1 

150-0 

30-25 

Chlorine 

1-9 

10-2 

I-QI 

N  as  nitrates 

o-ig 

O-OO 

0-18 

Thus  the  water  polluted  with  —^  per  cent,  of  the  crude  sewage 
taken  in  the  experiment  (or  i  gallon  of  sewage  to  i,ooo  gallons 
of  water)  shows  the  free  and  saline  ammonia  increased  about 
13  times,  the  albuminoid  ammonia  increased  by  not  much  over 
I  of  its  original  quantity,  the  total  solids  remain  practically  the 
same,  and  the  chlorine  shows  no  appreciable  increase. 

When  the  health  officer  has  to  make  periodical  examinations 
of  the  same  water,  it  will  not  be  necessary,  in  order  to  detect 
contamination,  always  to  perform  a  complete  analysis.  No 
object  will  be  gained,  for  instance,  by  the  estimation  of  the 
total  solid  matter  and  the  hardness;  but  one  must  never  neglect 


Il6  LABORATORY   WORK 

the  free  and  saline  ammonia  ligure,  which  is  of  paramount  im- 
portance. It  ma}-  be  said  with  certainty  that  in  such  cases  the 
shghtest  increase  of  ammonia  slioiild  be  regarded  with  grave 
suspicion. 

In  the  hght  of  a  chemical  anal3'sis  the  fitness  of  the  water  for 
drinking  purposes  will  be  determined  by  the  following  considera- 
tions: 

Is  any  evidence  forthcoming  of  animal  contamination  present 
or  past  ?  Is  there  evidence  of  excessive  ^•egetable  pollution  ? 
Is  the  nature  and  amount  of  the  saline  constituents  likely  to 
pro\'e  harmful  ?     Are  poisonous  metals  present  ? 

The  suitability  of  the  water  for  other  uses,  such  as  for  washing 
and  trade  purposes,  will  depend  upon  its  ligure  of  hardness,  the 
absence  of  a  marked  colour  and  freedom  from  suspended  or 
deposited  matter. 

The  evidence  of  present  or  recent  animal  pollution  is  more 
especially  indicated  by  high  chlorine  and  oxidized  nitrogen,  in 
association  with  marked  free  and  albuminoid  ammonia;  and  that 
of  past  or  remote  animal  pollution  by  high  clilorine  and  oxidized 
nitrogen  (not  accounted  for  by  the  strata  permeated)  with  little 
free  and  albuminoid  ammonia. 

If  the  pollution  is  solely  of  a  vegetable  origin  it  is  indicated 
by  high  figures  of  albuminoid  ammonia  and  of  oxygen  absorbed 
by  Tidy's  method,  in  association  with  very  low  figures  of  clilorine 
and  oxidized  nitrogen  in  the  case  of  surface  waters,  and  with 
practically  no  increase  in  these  latter  two  figures  if  the  water  is 
collected  from  below  the  surface.  Waters  containing  excessive 
vegetable  pollution  would  generally  be  coloured,  and  the  solid 
residue  would  char  considerably  upon  ignition.  As  to  excessive 
or  harmful  mineral  matter  in  a  drinking-water,  a  limit  of  lOO 
parts  per  100,000  ought  not  to  be  exceeded;  but  it  is  generally 
the  nature  of  the  mineral  matter  rather  than  its  amount  which 
will  affect  the  opinion.  Sulphates  should  not  furnish  more  than 
10  parts  of  SO3  per  100,000;  iron  is  only  permissible  when  in 
traces,  and  other  poisonous  metals  should  be  absent. 

A  water  containing  over  30  parts  of  hardness  may  be  regarded 
as  unfit  for  trade,  washing,  and  cooking  purposes.  It  is  rare 
with  these  waters  that  the  total  hardness  cannot  readily  be 
reduced  considerably  by  a  water-softening  process. 

A  few  examples  of  waters  from  difierent  sources,  together  with 
the  opinion  upon  them  which  the  chemical  analysis  (expressed 
as  parts  per  100,000)  appears  to  warrant,  may  now  be  given. 


THE    OPINION    ON    WATER    SAMPLES 


117 


Physical  characters 
Reaction 

Free  and  saline  ammonia.  . 

Albuminoid  ammonia 

O  absorbed  from  permanganate  (in  two 

hours  at  27°  C.) 
Total  solid  matters 

(a)  Volatile     .  . 

{b)   Fixed 

(c)    Appearance  on  ignition 

Total  hardness 

{a)  Temporary 

(6)   Permanent 
Chlorine 
N  as  nitrates 

Note. — ^Sample  2  is  evidently  a  chalk  water  contaminated  with  animal 
matter,  as  evidenced  by  the  high  ammonias  (the  "  free"  being  higher  than 
the  "albuminoid"),  and  the  high  figures  of  oxidized  nitrogen  and  chlorine 
(for  a  chalk  water) .  The  very  high  figure  of  free  and  saline  ammonia  points 
to  recent  and  therefore  specially  dangerous  contamination. 


1. 

2. 

A  wry  I'nre 

A  Foul  anfl 

WhId: 

Dangerous  Watur. 

Excellent 

Excellent 

Faintly 

Markedly 

alkaline 

alkaline 

o-ooi 

0'022 

0'002 

0-014 

0'0I2 

0-114 

l8-o 

38-4 

4-6 

18-1 

13-4 

20-3 

Nil 

Marked 

charring 

9-0 

24-0 

4-0 

16-0 

5-0 

8-0 

I'O 

6-2 

O'OI 

0-8 

Physical  characters 
Reaction 

Free  and  saline  ammonia 

Albuminoid  ammonia 

O  absorbed  from  permanganate  (in  two 

hours  at  27°  C.) .  . 
Total  solid  matters 

{a)  Volatile 

{b)   Fixed 

{c)    Appearance  on  ignition 

Total  hardness 

{a)  Temporary 

(&)    Permanent 
Chlorine 
N  as  nitrates 

Notes. — Sample  3.  In  industrial  towns  the  reaction  may  be  slightl}^  acid, 
from  the  sulphuric  acid  in  the  atmosphere;  and  the  water  is  a  little  different 
in  other  respects  owing  to  further  impurities  taken  up,  such  as  soot,  sulphur 
compounds,  and  increased  ammonia.  Thus  the  rain  falling  in  INIanchester 
has  been  found  to  contain  0-7  part  per  100,000  of  free  ammonia,  0-03  of 
albuminoid  ammonia,  4-7  parts  of  sulphuric  acid,  and  0-5S  of  hydrochloric 


3. 

4. 

Rain  Water 
(Country). 

Good 

Subsoil  Water 
(Gravel  over  Chalk) 

Good 

Faintly 
alkaline 

Alkaline 

0-050 

0-002 

0-005 

0-006 

0-005 

o-o6i 

3-0 

29-2 

1-5 

12-2 

1-5 

Nil 

17-0 

Slight 

charring 

0-5 

20-0 

o-o 

5"5 

0-5 

14-5 

0-25 

2-1 

0-02 

0-2 

ii8 


L\BOKATORY   WORK 


acid.  Rain  collected  on  the  sea  coast  has  been  found  to  contain  as  much 
as  5*4  parts  per  100,000  of  chlorine  (chlorides). 

Rain  water  which  is  collected  in  countr}'  districts  after  long  periods  of 
continuous  rainfall  provides  the  purest  possible  nahtral  water.  Its  com- 
position varies  throughout  the  year  somewhat. 

Sample  4.  The  analysis  does  not  furnish  evidence  of  harmful  contamina- 
tion; but  the  ammonias  suggest  the  presence  of  a  little  vegetable  matter. 


Physical  characters 

Reaction 

Free  and  saline  ammonia.  . 

Albuminoid  ammonia 

O  absorbed  from  permanganate 

hours  at  27°  C.)  .  . 
Total  solid  matters 

(«)  Volatile     .  . 

(6)   Fixed 

(c)    Appearance  on  ignition 


Total  hardness 

(a)  Temporary 
{b)   Permanent 

Chlorine 

N  as  nitrates 


(in  tw 


A  Peaty 
Surface  Water. 

Brownish- 
yellow 
Acid 
o-ooi 

0'022 

0'i6o 

I2"0 

9-5 

2-5 
Marked 
charring 

3.0 

o-o 

3-0 

0-7 

O'OI 


6. 

A  N on -peaty 

Surface  Water  on 

Millstone  Grit. 

Nearly 

colourless 

Neutral 

0'002 

0*004 

0-040 
5-5 

2-0 

3-5 
Faint  dis- 
coloration 

2-5 

O'O 

2-5 

0-8 
0-05 


Note. — In  many  "peaty  waters"  the  "organic  ammonia"  and  the 
"  oxygen  absorbed  "  will  be  found  to  much  exceed  the  amounts  given 
above.  Neither  of  the  above  analyses  furnishes  evidence  of  harmful  con- 
tamination. 


Physical  characters 

Reaction 

Free  and  saline  ammonia.  . 

Albuminoid  ammonia 

O  absorbed  from  permanganate 

hours  at  27°  C.) .  . 
Total  solid  matters 

{a)  Volatile     .  . 

{b)   Fixed 

(c)    Appearance  on  ignition 


Total  hardness 

(a)  Temporary 
(6)   Permanent 

Chlorine 

N  as  nitrates 


in  tw 


7. 

Deep-well  Water 
(from  Chalk). 

Excellent 

Alkaline 

0'Oo6 

O'OII 

0'oS4 

40-0 

15-5 

24-5 
Marked 
charring 

26*0 

15-5 

TO-5 

4-5 
0-6 


8. 

Deep-well  Water 

(from  New  Red 

Sandstone). 

Good 

Alkaline 

o-ooi 

0'002 


0'0I2 

30-2 
8-6 

21'6 

Nil 

19-5 
8-0 

"•5 

2-2 
0.3 


THE    OPINION    ON    WATER    SAMPLES 


119 


Notes. — A  deep-well  water  from  the  chalk  may  (  ontain  total  solids  up  to 
200  parts  per  100,000,  but  such  an  amount  is  rare. 

Sample  7  is  a  water  the  analysis  of  which  warrants  suspicion  of  organic 
contamination.  Slight  animal  contamination  is  probable  in  such  a  water, 
having  regard  to  the  figures  of  the  saline  and  albuminoid  ammonia,  the 
chlorine  and  the  oxidized  nitrogen.  A  careful  local  inspection  might 
detect  the  source  of  some  pollution. 

There  is  no  reason  to  question  the  purity  of  Sample  8. 


Physical  characters 
Reaction 

Free  and  saline  ammonia.  . 

Albuminoid  ammonia 

O  absorbed  from  permanganate 

hours  at  27°  C.)  .  . 
Total  solid  matters 

{a)  Volatile     .  . 

{b)   Fixed 

(c)    Appearance  on  ignition 


Total  hardness  . . 
(a)  Temporary 
{b)   Permanent 

Chlorine 

N  as  nitrates 


9. 

10. 

River  Water. 
Good 

New  River  Water 

(as  supplied  in 

London). 

Excellent 

Faintly 
alkaline 

Faintly 
alkaline 

O'oog 

O'OOI 

0-017 

0'002 

o-ogg 

0-014 

32-5 

31-5 

i4'0 

9-0 

..        i8-5 

Marked 

22-5 

Nil 

charring 

20-5 

22-0 

9-0 

8-5 

II-5 

2-4 

13-5 
1-8 

0-4 

0-2 

Notes. — Sample  9.  The  composition  of  river  water  will  alwaj^s,  of  course, 
vary  with  the  following  circumstances : 

1.  The  nature  of  the  country  through  which  the  river  courses,  and 
which  it  therefore  drains — i.e.,  whether  this  be  cultivated  and  manured 
or  wild,  whether  there  be  much  or  little  vegetation,  and  whether  it  be 
thickly  or  sparsely  populated. 

2.  The  amount  of  pollution  by  sewage,  waste  products  of  manufactories, 
etc.,  which  gain  access  to  the  water. 

3.  The  nature  of  the  bed  of  the  river,  and  of  the  strata  through  which 
any  springs  (which  feed  the  river)  rise. 

4.  The  rapidity  and  smoothness  of  flow — i.e.,  the  more  rapid  and  inter- 
rupted this  is,  the  greater  the  powers  of  the  river  in  the  direction  of  self- 
purification. 

No.  9  furnishes  evidence  of  contamination. 
No.  10  is  a  water  of  great  purity. 


120 


LABORATORY   WORK 


11. 


12. 


Jjeep  spring  w.iter 

(from  Green'vand 

below  Chalk). 

Spring  Water 
(from  Chalk). 

Physical  characters 

.  .      Excellent 

Excellent 

Reaction 

Alkaline 

Alkaline 

Free  and  saline  ammonia. . 

0-030 

O'OOI 

Albuminoid  ammonia 

O'OOI 

0-003 

O  absorbed  from  permanganate 

(in  two 

hours  at  27°  C.) 

0'020 

O'Oig 

Total  solid  matters 

III'2 

32-5 

(a)  Volatile     .  . 

21'0 

8-5 

{b)   Fixed 

90'2 

24-0 

(c)   Appearance  on 

ignition  . 

..Nil 

Nil 

Total  hardness 

..        i8-5 

23-0 

(a)  Temporary' 

..          7-0 

i8-o 

{b)   Permanent 

II-5 

5-0 

Chlorine 

12-2 

3-0 

N  as  nitrates 

..0.4 

0'2 

Notes. — In  Sample  11  the  high  amounts  of  saline  ammonia,  chlorine  and 
mineral  matter  so  frequently  present  in  pure  waters  from  the  lower  green- 
sand,  are  shown.  Sometimes  the  nitrates  are  higher  than  in  this  sample. 
The  absence  of  recent  animal  pollution  in  this  case  is  shown  by  the  very 
low  figure  of  albuminoid  ammonia. 

Sample  12  is  a  very  pure  water.     The  ammonias  are  quite  low. 


13. 

14. 

Well  Water  from    " 

Carboniferous 

Well  Water. 

Limestone. 

Physical  characters 

E.xcellent 

Excellent 

Reaction 

Alkaline 

Alkaline 

Free  and  saline  ammonia.  . 

0-005 

O-OOI 

Albuminoid  ammonia 

0-006 

O-OOI 

0  absorbed  from  permanganate 

(in  two 

hours  at  27°  C.) 

0-066 

0-008 

Total  solid  matters 

31-9 

48-5 

{a)  Volatile     .  . 

9-8 

17-3 

(b)    Fixed         

22-1 

31-2 

(c)   Appearance  on  ignition . 

.  .        Slight 
charring 

Nil 

Total  hardness 

24-2 

31-5 

(a)  Temporary 

17-9 

9-5 

{b)   Permanent 

6-3 

22-0 

Chlorine 

1-9 

6-2 

N  as  nitrates 

0-3 

1-8 

Notes. — Sample  13.  The  ammonia  figures  indicate  slight  animal  con- 
tamination. 

Sample  14  furnishes  evidence  of  previous  (remote)  sewage  contamination 
in  the  high  figures  of  N  as  nitrates  and  chlorine.  The  extremely  low 
albuminoid  ammonia  figure  shows  that  the  organic  matter  has  been  almost 
completely  mineralized.  Nitrites  were  absent,  but  phosphates  were 
markedly  present. 


THE    OPINION    ON    WATER    SAMPLES 


121 


15. 

16. 

Chalk  Water. 

Peaty  Water. 

Excellent 

Light  brown 

tint;  clear 

Alkaline 

Acid 

O'OiS 

0-005 

O-OIO 

0-022 

0-082 

0-122 

62-7 

15-6 

23-2 

12-0 

39-5 

3-6 

Marked 

Marked 

charring 

charring 

33-5 

3-0 

22*5 

o-o 

II-O 

3-0 

6-8 

1-5 

0-9 

0'2 

Physical  characters 

Reaction 

Free  and  saline  ammonia. 

Albuminoid  ammonia 

O  absorbed  from  permanganate  (in  two 

hours  at  27°  C.) 
Total  solid  matters 

{a)  Volatile     .  . 

lb)   Fixed 

(c)    Appearance  on  ignition 

Total  hardness 

(a)  Temporary 

(6)   Permanent 
Chlorine 
N  as  nitrates 

Notes. — Sample  15  is  a  chalk  water  polluted  with  animal  matter,  as 
evidenced  by  the  high  saline  ammonia  (along  with  a  considerable  amount 
of  organic  ammonia)  and  the  high  figures  of  chlorine  and  oxidized  nitrogen. 
The  hardness  is  also  excessive,  but  this  may  readily  be  reduced  to  11  parts 
by  a  water-softening  process. 

Sample  16  is  a  peaty  water  polluted  with  animal  matter,  as  evidenced 
by  the  fact  that  the  figures  of  the  saline  ammonia,  the  chlorine,  and  of  the 
oxidized  nitrogen,  are  excessive  for  a  peaty  water.     It  is  a  water  possessing 
a  considerable  plumbo-solvent  action. 

17. 
Physical  characters  . .  . .  . .       Brackish 

•  taste ;   blue- 

green  tint 

Reaction Alkaline 

Free  and  saline  ammonia.  .  ..  ..  o-ooi 

Albuminoid  ammonia        .  .  . .  .  .  0-006 

O  absorbed  from  permanganate  (in  two 

hours  at  27°  C.) . 


18. 

Excellent 


Alkaline 
0-004 
0-005 


Total  solid  matters 

(a)  Volatile 

(&)   Fixed         

(c)    Appearance  on  ignition . 


Total  hardness 

{a)  Temporary 
(6)   Permanent 

Chlorine 

N  as  nitrates 


0-050 
249-2 
32-8 
216-4 
Slight  dis- 
coloration 
Very  high 


109-5 
0-9 


0-042 

34'0 

ii-o 

23-0 
Faint  dis- 
coloration 

23-5 
13-0 
10-5 

1-9 

0.3 


Notes. — Sample  17  is  a  deep-well  water  in  the  chalk  contaminated  by 
sea  water.  This  is  evidenced  by  the  fact  that  the  chlorine  is  enormously 
high  and  magnesium  chloride  is  abundant.     The  well  was  near  the  coast 


122  LABORATORY    WORK 

and,  prior  to  the  contamination,  the  chlorine  was  4  parts  per  100,000  and 
the  total  hardness  24.  The  water  is  quite  unfit  for  domestic  uses  on  account 
.  of  its  excessive  hanlness,  the  brackish  taste,  the  deposit  it  will  give  rise  to 
in  boilers  and  kettles,  and  the  fact  that  it  will  impair  the  palatability  of 
tea,  coffee,  etc.;  and  it  is  altogether  unsuitable  for  washing  and  cooking 
purposes. 

Sample  18  is  a  polluted  water.  The  above  figures  would  barely  warrant 
such  an  opinion,  but  a  previous  analysis  of  the  water  from  the  same  source 
gave  the  saline  and  organic  ammonias  as  0-002  and  0-003  respectively, 
and  the  chlorine  and  oxidized  nitrogen  as  i-S  and  0-20  respectively.  Some 
pollution  has  therefore  recently  gained  access  to  the  water,  and  the  sample 
is  included  to  illustrate  the  value  of  periodical  analyses  of  a  water-supply 
in  detecting  intermittent  pollution. 

An  examination  of  the  bed  of  a  waterway  or  pond  may  serve 
to  furnish  corroborative  evidence  of  the  sewage  contamination  of 
the  water.  Of  such  contamination  there  is  httle  or  no  reliable 
indication  by  chemical  anatyses,  nor  does  a  low-power  micro- 
scopic examination  and  a  bacteriological  examination  supply 
valuable  evidence;  and  unless  the  pollution  is  gross,  it  is  not 
possible  to  conclude  that  a  mud  is  contaminated  with  human 
excrement,  either  from  chemical  or  bacteriological  data. 

If  any  parts  of  the  bed  are  covered  with  gravel  or  large  stones 
which  are  not  clean,  and  especially  if  the  greyish  flocculent 
growths  characteristic  of  certain  sewage  fungi  are  found  to  be 
attached  to  them  or  to  any  other  part  of  the  bed,  and  if  the  mud 
is  of  a  dark  colour  and  emits  gas  bubbles  and  offensive  odour 
on  being  disturbed,  then  there  are  good  reasons  for  suspecting 
gross  sewage  contamination.  It  is  common  in  these  circum- 
stances to  find  some  opalescent  floating  bubbles,  which  have  but 
little  tendency  to  burst,  on  parts  of  the  surface  of  the  overlying 
\\ater. 

Although  the  organic  matter  in  pond  and  river  mud  will  be 
found  on  an  ordinary  microscopical  examination  to  be  largely 
in  the  form  of  unrecognizable  debris,  with  only  a  relatively  small 
(but  variable)  quantity  of  the  vegetable  structure  of  plant  life 
distinguishable,  a  textile  fibre  or  animal  hair,  etc.,  \\'ould  indicate 
dangerous  contamination  {vide  p.  155). 

Water  markedly  contaminated  with  sewage  or  sewage  effluent 
is  unlit  to  be  used  by  cows  for  drinking  purposes;  for,  apart  from 
the  risk  to  the  health  of  the  animal,  there  is  a  danger  of  specific 
organisms  of  intestinal  origin  getting  upon  the  teats  and  udders 
of  the  cows,  and  thereby  into  the  milk  in  the  process  of  milking. 

Gerber   and   Sheldon   botli    agree  that    dirty   drinking-water 


THE    OPINION    ON    WATER    SAMPLES  123 

may  give  rise  to  impure  and  tainted  milk.  We  know  that 
improper  food,  such  as  fermented  potatoes  or  cabbages,  affect 
the  taste  and  keeping  quahties  of  cow's  milk;  and  there  is  no 
reason  why  what  applies  to  food  should  not  apply  to  drink. 
It  is,  moreover,  only  reasonable  to  suppose  that  the  drinking  of 
polluted  water  is  injurious  to  the  cow  as  well  as  to  the  milk;  and 
that  the  purer  the  food  and  water  given  to  cows  tlie  better  both 
for  the  animal  and  for  the  milk  she  furnishes. 

The  presence  of  a  small  amount  of  domestic  sewage  in  a  stream 
of  fair  volume  and  flow  is  apparently  not  injurious  to  fish. 
Oysters,  mussels,  and  cockles  are  tolerant  of  considerable  sewage 
pollution,  although  there  is  evidence  that  oysters  become  scarcer 
and  smaller  in  the  presence  of  gross  pollution;  but  in  the  case 
of  these  shellfish,  their  capacity  to  retain  specific  disease-pro- 
ducing bacteria  when  bathed  in  polluted  water  makes  the  con- 
sumption of  them,  when  collected  from  such  waters,  a  grave 
danger,  the  reality  of  which  has  been  abundantly  demonstrated 
in  this  and  other  countries. 

Fresh-water  fish  generally  are  more  affected  by  pollution  from 
chemical  wastes  than  by  sewage;  but  they  vary  considerably  in 
their  susceptibihty  to  sewage  contamination.  In  experimenting 
upon  the  effect  of  the  sewage  contamination  of  a  stream  upon 
fish  life,  allowance  must  be  made  for  this  fact.  Trout  appear  to 
be  very  susceptible,  and  they  require  to  be  kept  in  running 
water.  Gold-fish,  gudgeon,  and  roach  (of  which  the  latter  two 
are  very  sensitive  to  various  forms  of  pollution  in  water,  while 
the  former  is  relatively  resistant)  are  suitable  fish  to  experi- 
ment with.  These  may  be  kept  in  the  contaminated  water, 
while  at  the  same  time  control  fishes  are  kept  in  pure  water; 
and  by  observation  of  their  active  movements,  their  food  con- 
sumption, the  healthy  appearance  of  their  eyes,  fins,  tails,  etc., 
the  weight  of  the  survivors  at  the  end  of  the  experiment,  and 
the  rate  of  mortality,  it  is  not  difficult  to  learn  from  the  com- 
parative data  collected  whether  the  polluted  water  has  proved 
inimical  or  not. 

Bacteriological  Evidence. 

Like  the  chemical,  the  value  of  this  evidence  has  certain 
limitations.  As  ordinarily  performed,  even  the  bacterial  counts 
furnish  evidence  only  of  the  discrete  masses  of  organisms.  There 
is  no  necessary  relationship  between  these  and  the  numbers  of 


124  LABOKATOKY    WORK 

separate  organisms  originally  present,  because  with  efflux  of 
time  the  organisms,  like  other  suspended  particles,  tend  to 
agglutinate.  Again,  at  the  present  day  it  is  often  impossible  to 
reco\ier  or  recognize  the  specific  germ,  even  shortly  after  this  has 
been  experimentally  added  to  water;  and  the  organisms  which 
denote  sewage  contamination  are  the  same  whether  they  are 
derived  from  the  lower  animals  or  from  human  beings.  Yet, 
despite  these  facts,  the  results  of  a  bacteriological  examination 
of  water  samples,  interpreted  in  the  light  of  topographical  cir- 
cumstances, is  generally  of  great  value. 

The  Colleciion  and  Transmission  of  Samples. — Great  care  is 
required  in  the  collection  of  the  samples;  even  apparently  trivial 
errors  or  omissions  may  entirely  vitiate  the  result.  Very  precise 
and  seemingly  trifling  directions  must  be  given,  unless  the  sample 
is  collected  by  an  expert. 

For  the  ordinary  examination  2-ounce  (57  c.c.)  glass-stoppered 
bottles  are  sufficient.  When  larger  amounts  are  required,  a 
Winchester  quart  bottle  may  be  used.  The  bottles  should  be 
sterilized,  with  their  stoppers  loosely  inserted,  at  160°  C.  for  one 
hour,  and  allowed  to  cool  slowly. 

If  the  specimen  cannot  be  examined  at  once,  and  delay  is 
unavoidable,  the  sample  should  be  packed  in  ice,  and  then  trans- 
mitted to  the  laboratorj^  Special  apparatus  have  been  designed 
for  this  purpose. 

That  figured  on  p.  125  is  a  convenient  form.  Two-ounce 
glass-stoppered  bottles  are  used.  Each  of  these,  after  thorough 
washing,  and  drying  in  the  hot-air  apparatus,  has  its  stopper 
inserted,  and  is  then  placed  in  a  tin  into  which  it  just  shps. 
The  bottom  of  the  tin  has  a  layer  of  cotton-wool  and  then  a 
piece  of  asbestos  cardboard. 

Several  thicknesses  of  asbestos  cardboard  are  also  fitted  in 
the  cover  of  the  tin,  so  that  when  in  place  the  bottle  is  firmly  in 
contact  with  the  asbestos  above  and  below.  The  tins  with  their 
contained  bottles  are  then  sterilized  in  the  hot-air  apparatus- 
Labels  are  placed  on  the  outside  of  the  tins,  and  they  are  ready 
for  use.  The  ice-boxes  are  made  to  just  receive  one,  two,  or 
four  such  tins.  The  tins  are  not  opened  after  sterilization  until 
immediately  before  the  sample  is  taken. 

To  take  samples  from  various  depths,  a  number  of  different 
forms  of  apparatus  have  been  devised.  The  ordinary  collecting- 
bottle  may,  however,  be  also  used  for  this  purpose.     It  is  tied 


BACTERIOLOGICAL   EVIDENCE 


125 


into  a  leaden  cage,  and  lowered  to  the  required  depth  by  catgut 
or  string  attached  to  the  cage.  The  loosened  stopper  is  then 
removed  by  a  jerk  upon  a  second  string  previously  tied  to  the 
stopper,  and  the  sample  collected. 

In  collecting  samples  from  a  reservoir,  lake,  or  river,  plunge 
below  the  surface  before  removing  the  stopper,  thus  avoiding 
scum  and  surface  contaminations.  If  from  a  tap,  allow  the 
water  to  first  run  to  waste  for  five  to  ten  minutes.  If  from 
wells  with  a  pump,  pump  away  a  considerable  quantity  of  water 


FIG.   l6. COLLECTING- 
BOTTLE    AND    TIN. 

A,  Asbestos  cardboard  in  lid; 
B,  asbestos  cardboard  below 
bottle  D  ;  C,  cotton-wool 
layer. 


FIG.    17. ICE-BOX. 

A  and  B,  felt  lining;  C,  metal  ice  re- 
ceptacle, with  depression  D,  to  hold 
two  collecting-tins  (with  contained 
bottles) . 


before  collecting  the  sample;  while  if  a  complete  investigation 
is  required,  a  second  sample  should  be  obtained  after  several 
hours'  pumping. 

Owing  to  the  extreme  difficulty  of  detecting  the  actual 
specific  organisms  of  disease,  such  as  the  organisms  of  typhoid 
fever  and  cholera,  it  is  necessary  to  resort  to  other  methods  of 
investigation. 

Hygienists  are  unanimous  in  recognizing  that  sewage  and  the 
excreta  of  human  beings,  diseased  or  healthy,  must  be  looked 
upon  as  potential  vehicles  for  disease  production.     The  presence 


126  LABORATORY    WORK 

of  the  excreta  of  animals  must  also  be  looked  upon  as  prejudicial, 
since  it  may  contain  harmful  bacteria  and  other  parasites. 

A  number  of  organisms  have  been  advocated  as  fulfilling  the 
requirements  necessary  for  indicators  of  sewage  contamination. 
Of  these,  B.  coli  and  allied  organisms,  B.  ententidis  sporogenes, 
and  certain  streptococci,  are  the  only  ones  which  have  been 
extensively  advocated  and  merit  detailed  consideration. 

For  these  organisms  it  is  not  only  necessary  to  ascertain  their 
presence  or  absence,  but,  in  addition,  their  numbers. 

Significance  and  Interpretation  of  Results. — The  detection  of  the 
cholera  spirillum  or  the  typhoid  bacillus  in  a  water,  in  whatever 
amount,  is  sufficient  to  condemn  the  water.  The  other  results 
obtained  in  the  bacteriological  examination  of  water-supplies  are, 
however,  only  data  from  which  an  opinion  upon  the  purity  or 
contamination  of  the  water  can  be  deduced  with  more  or  less 
confidence  according  to  the  data  available. 

Such  deductions  require  much  special  experience,  and  for  a 
detailed  consideration  of  the  matter  the  reader  is  referred  to 
Dr.  Savage's  book  on  the  subject,*  limits  of  space  only  allowing 
here  a  bald  summar}'  and  review. 

The  number  of  organisms  developing  upon  gelatine  plates  is 
largely  an  index  of  the  amount  of  organic  matter  in  the  water, 
although  there  is  no  constant  or  exact  relationship  between  the 
two.  Still,  the  addition  of  organic  matter  almost  invariably 
means  an  addition  both  of  foreign  bacteria  and  of  material 
which  enables  the  water,  for  a  time  at  least,  to  become  a  better 
nutrient  medium,  and  so  causes  an  increased  proliferation  of 
bacteria. 

A  low  gelatine  count  is,  therefore,  a  satisfactory  feature;  but, 
on  the  other  hand,  a  high  gelatine  count  cannot  in  itself  be  con- 
sidered a  sufficient  reason  for  condemning  a  water.  For  surface 
waters  the  contamination  is  frequently  with  harmless  organic 
matter,  and  of  comparative  unimportance. 

Good  deep-well  and  spring  waters  frequently  contain  less  than 
50  bacteria  per  c.c.  developing  on  gelatine  plates,  while  in  surface 
waters,  even  when  free  from  pollution,  up  to  500  or  more  per  c.c. 
are  not  infrequently  met  with. 

The  blood-heat  count  (agar  plates  at  37°  C.)  is  an  index  of  the 
addition  of  bacteria  other  than  those  natural  to  pure  water,  but 

*  "  The  Bacteriological  Examination  of  Water-Supplies  "  (H.  K.  Lewis, 
London,  1906). 


BACTERIOLOGICAL   EVIDENCE  I27 

they  need  not  be  harmful.  The  addition  of  harmless  soil  bacteria 
will  cause  a  great  increase  in  the  number  of  the  ^Y'  ^^-  organisms. 
The  number  present  in  deep-water  sources,  when  pure,  is  very 
low,  frequently  less  than  i  per  c.c,  and  10  or  more  per  c.c.  is 
not  satisfactory.  In  the  case  of  surface  waters  and  rivers,  soil 
washings  are  common,  and  a  more  generous  margin  (50  to  100 
per  c.c.)  is  necessary.  On  the  whole,  a  marked  increase  in  the 
number  of  bacteria  growing  at  37°  C.  is  of  greater  significance 
than  a  proportionate  increase  of  the  gelatine  count. 

Of  much  greater  importance  is  the  interpretation  of  the  B.  coli 
estimation.  The  views  of  different  workers  show  considerable 
variance.  This  bacillus  is  abundant  in  human  and  animal 
excreta  and  in  sewage,  and  it  serves  as  a  meas^ure  of  excretal 
pollution. 

Deep-well  and  spring  water  should  not  be  liable  to  any  poUu- 
tion  by  material  containing  B.  coli.  Water  from  these  sources, 
even  if  originally  polluted,  must  have  passed  through  a  con- 
siderable depth  of  soil,  and  thus  have  become  purified  from  all 
bacterial  evidence  of  contamination.  If  such  sources  are  properly 
protected  at  their  outlets,  there  is  no  reason  why  they  should 
contain  any  B.  coli.  It  is,  therefore,  justifiable  to  maintain  an 
attitude  of  great  suspicion  towards  any  water  from  such  sources 
which  contains  B.  coli  in  100  c.c.  or  less. 

In  the  case  of  surface  supplies  and  shallow  wells  the  position 
is  different.  For  example,  considering  upland  surface  waters, 
the  opportunity  for  contamination  by  B.  coli  contained  in  animal 
{e.g.,  sheep)  excreta  may  be  considerable.  The  B.  coli  from 
sheep  excreta  are  indistinguishable  from  those  from  sewage  or 
human  feeces,  yet  no  one  would  contend  that  they  are  of  equal 
significance,  or  that  it  is  equally  important  to  prevent  their 
presence. 

As  a  matter  of  experience,  on  the  other  hand,  it  will  generahy 
be  found  that  B.  coli  rigidly  defined  is  not  found  in  shallow  wehs, 
or  in  the  majority  of  surface  supplies,  in  10  c.c.  or  less,  unless 
that  water  is  being  polluted  with  excrementitious  matters  in 
undesirable  amount. 

While,  therefore,  admitting  that  dogmatic  standards  are 
especially  untrustworthy  for  these  classes  of  waters,  a  working 
standpoint  that  the  finding  of  excretal  B.  coli  in  10  c.c.  or  less  points 
to  undesirable  pohution  is  both  justifiable  and  in  accordance 
with  actual  experience.     If  no  B.  coli  are  present  in  50  c.c.  the 


128  LABORATORY   WORK 

water  ma}-  be  safely  passed  as  satisfactory.  For  rivers  used  as 
sources  of  drinking-water,  without  artificial  purification,  similar 
standards  are  applicable. 

Sometimes  the  organisms  isolated  are  not  typical  B.  coli,  but 
differing  in  the  absence  of  one  or  more  of  the  characteristic 
properties  of  this  organism.  In  the  opinion  of  most  bacteriolo- 
gists of  experience  the  nearer  these  lactose-fermenting  coli-like 
bacilli  approach  typical  B.  coli  in  their  characters,  the  more 
nearly  are  our  numerical  standards  for  that  organism  applicable 
to  them,  while  if  the}'  lack  essential  characters  a  proportion- 
ately greater  number  must  be  present  to  justify  an  adverse 
opinion. 

Determinations  of  the  number  of  streptococci  have  been  made 
much  less  frequently  than  in  the  case  of  B.  coli.  As  a  pro- 
visional guide,  and  without  attaching  an  equal  significance  to 
the  findings,  a  standard  similar  to  that  for  B.  coli  may  be  em- 
ployed— i.e.,  their  presence  in  lOO  c.c.  or  less  of  deep-well  or 
spring  water,  or  in  lo  c.c.  or  less  of  surface  and  shallow-well 
waters,  would  justify  an  adverse  opinion  as  to  the  purity  of  the 
water  in  question. 

On  its  negative  side  the  streptococcus  test  is  not  of  great 
value,  and  the  absence  of  streptococci,  even  in  a  considerable 
bulk  of  water,  cannot  be  taken  as  showing  purity  or  freedom 
from  danger. 

Opinion  is  not  united  as  to  the  value  of  B.  enterilidis  sporo- 
genes  as  an  indicator  of  pollution.  It  is  fairly  abundant  in 
sewage  and  excreta,  but  it  is  a  spore-bearing  organism  with 
prolonged  powers  of  resistance,  and  therefore,  even  if  it  be 
admitted  that  its  presence  indicates  pollution,  such  pollution 
may  have  taken  place  at  some  long  antecedent  period,  a  con- 
tamination so  old  as  to  be  of  no  significance.  But  its  absence 
in  a  large  quantity  of  water  is  some  evidence  of  purity. 

It  will  be  of  assistance  in  the  difficult  matter  of  giving  an  opinion  upon 
samples  submitted  for  bacteriological  examination  if  a  few  examples  are 
given  of  samples  from  different  sources.  They  represent  actual  analyses, 
in  which  the  topographical  conditions  were  accurately  investigated  either 
at  the  time  of  examination  or  subsequently. 

I.  An  upland  surface  water  collected  in  an  open  artificial  reservoir: 
Number  of  organisms  developing  per  c.c.  at  37°  C.=    16. 

2I°C.=  224. 

"  Excretal  "  B.  coli  present  in  40  c.c,  but  not  in   10  c.c.  or 

smaller  amounts. 
Streptococci  absent  in  50  c.c. 


BACtERlOLOGICAL   EVIDENCE  I29 

(Standard+i  media;  incubation  lorty-two  liours  at  37'  C,  three  days 
at  21°  C.) 

The  bacteriological  opinion  from  this  sample  would  be  favourable. 
Careful  topographical  investigation  showed  no  evidence  of  any  human 
sources  of  infection  on  the  gathering  ground,  but  the  water  was  liable  to 
some  pollution  from  sheep's  droppings,  etc. 

2.  A  mountain  stream  feeding  a  large  upland  surface  reservoir: 

Number  of  organisms  developing  per  c.c.  at  37°  C.  =  340. 

21°  C.  =  1,640. 
"  Excretal  "  B.  coli  isolated  from  10  c.c,  but  not  found  in 

smaller  quantities  of  the  sample. 
Atypical  B.  coli  isolated  from  i  c.c. 
Streptococci  present  in  30,  10,  and  i  c.c,  but  not  in  o-r  c.c. 

The  bacteriological  evidence  is  here  sufficient  to  condemn  the  water, 
and  topographical  investigation  showed  considerable  opportunities  for 
pollution  from  both  inhabited  houses  and  manured  lands. 

3.  A  surface  (shallow  well)  provided  with  a  pump: 

Number  of  organisms  developing  per  c.c.  at  37°  C.  =  ii2. 

21°  C.  =  7,700. 
"  Excretal  "  B.  coli  isolated  from  i  c.c,  but  not  from  o-i  c.c. 
Atypical  B.  coli  isolated  from  o-i  c.c. 
Streptococci  present  in  40  c.c,  but  not  in  10  or  i  c.c. 

The  well  is  evidently  polluted,  and  was,  in  fact,  surrounded  by  manured 
ground,  while  the  covering  to  prevent  surface  water  gaining  access  was 
defective,  and  there  was  no  internal  rendering  of  the  sides  of  the  well. 

4.  A  surface  well  provided  with  a  pump : 

Number  of  organisms  developing  per  c.c.  at  37°  C.  —  g. 

,.  ..      21°  C.=  7io. 

B.  coli  absent  in  50  c.c. 
Streptococci  absent  in  50  c.c. 

Here  the  examination  showed  no  evidence  of  any  harmful  contamination. 

The  well  was  situated  in  a  town,  and  was  surrounded  by  houses,  but 
surface  water  was  prevented  from  entering.  From  the  topographical 
position  it  was  impossible  to  say  whether  the  water  was  polluted  or  not. 

5.  A  spring  used  as  a  public  supply: 

Number  of  organisms  developing  per  c.c.  at  37°  C.  =  i. 

,,      2i°C.=34. 
B.  coli  absent  in  50  c.c 
Streptococci  absent  in  50  c.c. 

The  bacteriological  results  are  quite  satisfactory,  and,  indeed,  showed 
very  little  variation  at  each  monthly  examination. 

Careful  investigation  of  the  source  showed  no  likely  sources  of  contamina- 
tion, but  remote  sources  of  pollution  were  possible,  and  systematic  bacteri- 
ological examinations  were  very  valuable. 

N.B. — The  foregoing  information  under  "  Bacteriological  Evidence  " 
is,  in  the  main,  summarized  from  a  contribution  by  Dr.  W.  G.  Savage 
to  previous  editions  of  this  book. 

9 


CHAPTER  XV 


SEA  WATER 

The  Rivers  Pollution  Commissioners  found  that  sea  water  con- 
tains approximately: 

Parts  per  :oo,ooo. 

Total  solids       ..  ..  ..  ..     38987 

Chlorine  .  .  .  .  . .  .  .     1975  "6 

A  specimen  collected  by  the  late  Dr.  Tidy  during  high  water 
at  Margate  gave : 

Parts  per  ioo,ooo. 

Total  solids 


1.  VJLCXl     ;3W1H_IJ 

Chlorine 

..     1770-5 

Lime 

35-1 

Magnesia 

205-6 

Silica 

0-4 

Hardness 

. .      564-0 

As  edible  sea  shellhsh,  reared  or  deposited  round  our  shores, 
are  sometimes  exposed  to  dangerously  contaminated  sea  water, 
and  sea  water  contaminated  with  human  excrement  has  on  good 
grounds  been  helS  to  be  responsible  for  the  infection  of  enteric 
fever,  it  is  desirable  to  learn  what  evidence  is  available  of  the 
sewage  pollution  of  sea  water. 

A  summary  of  our  present  position  with  reference  to  bacterio- 
logical evidence  of  contamination  will  serve  to  indicate  the  value 
of  the  assistance  of  chemical  standards.  Although  the  Royal 
Commission  on  Sewage  Disposal,  appointed  in  1898,  reported 
that  they  were  satisfied  that  bacteriology  could  not  at  present 
be  relied  upon  to  determine  whether  or  not  shellfish  are  polluted 
by  sewage,  typical  Bacilli  coli  communis  in  shellfish  are  usually 
regarded  as  sufficient  evidence  of  such  pollution;  and  in  sea 
water,  Houston,  Hewlett,  Klein,  and  others  would  take  B.  coli 
communis  in  i  c.c.  as  indicating  contamination.     Dr.  Houston's 

130 


SEA   WATER  13 1 

work  for  the  Commissioners,  which  was  pubhshed  in  their  Fourth 
Report,  vol.  iii.,  1904,  clearly  shows  that  no  sample  of  sea  water 
remote  from  pollution  contains  either  B.  coli  communis  or  the 
spores  of  B.  enteritidis  sporogenes,  even  when  as  much  as  100  c.c. 
of  the  samples  are  used  for  test  purposes.  But  birds  and  fish 
may  contribute  B.  coli  communis  ;  and  he  suggests  the  prudence 
of  not  pushing  an  extremely  delicate  test  too  far.  He  further 
demonstrates  that  B.  coli,  added  to  sea  water,  is  no  longer  in 
evidence  in  i  c.c.  of  the  sample  after  a  maximum  period  of  nine 
days  and  a  minimum  period  of  five  days.  He  therefore  con- 
cludes that  absolute  standards  cannot  be  laid  down  at  present; 
but  he  maintains  that  B.  coli  present  in  10  c.c.  and  absent  in 
I  c.c.  should  be  viewed  with  some  degree  of  suspicion,  the  water 
not  necessarily  to  be  condemned  apart  from  topographical  and 
epidemiological  considerations. 

Such  vegetable  growths  as  Ulva  latissima  are  not  delicate  indi- 
cators of  sewage  pollution,  for  they  may  not  be  in  evidence  in 
cases  where  sea  water  is  exposed  to  the  lesser  degrees  of  con- 
tamination. 

Of  course,  gross  contamination  is  unmistakable  when  sea 
water  is  judged  from  the  results  of  either  a  bacteriological  or 
chemical  examination;  but  it  is  the  evidence  of  previous  and 
relatively  slight  contamination  that  may  be  ill-defined  and 
elusive.  Coast-tides,  currents,  and  eddies  are  capable  of  con- 
veying sewage  contamination  for  some  distance  from  the  actual 
outfall  of  sewage  into  the  sea  to  parts  where  there  is  no  local 
contamination  added,  and  there  is  nothing  to  indicate  such  pol- 
lution. A  period  of  twenty-four  hours  would  suffice  for  this 
contamination,  in  a  very  dilute  form,  to  reach  several  miles  from 
its  outfall;  and  laboratory  experimentation  indicates  that  the 
B.  typhosus  can  survive  several  days  in  sea  water. 

The  writer  and  F.  N.  Kay  Menzies  find  that  the  chemical 
evidence  upon  which  opinions  are  based  as  to  the  purity  or 
otherwise  of  the  various  classes  of  fresh  waters  is  not  wholly 
applicable  to  sea  water  after  slight  contamination  with  sewage, 
and  they  conclude  as  follows: 

While  the  chlorine  figure  is  often  a  useful  one  for  indicating 
animal  contamination  m  fresh  waters,  it  is  useless  in  respect  of 
sea  water,  for  the  reason  that  a  relatively  small  amount  of 
sewage  (with  an  average  chlorine  figure  of  about  10  parts  per 
100,000),  discharging  into  a  large  volume  of  sea  water  (with  a 


132  LABORATORY   WORK 

chlorine  figure  which  may  vary  from  i,6oo  to  over  1,900  parts 
per  100,000),  has  not  sufficient  effect  upon  the  chlorine  figure  of 
the  sea  water  to  furnish  e^ddence  of  sufficient  delicacy. 

The  oxidized  nitrogen  figure  is  even  more  serviceable  than 
the  chlorine  as  a  clue  to  the  previous  animal  contamination  of 
fresh  waters ;  for  in  fresh  waters  a  little  (say  i  per  cent.)  of 
sewage  contamination  leads  to  a  rapid  appearance  of  nitrates; 
but  when  sewage  effluent  with  already  formed  nitrates  is  added 
to  a  fresh  water,  there  is  generally  an  initial  reduction  of  the 
nitrates  (often  lasting  for  two  or  three  weeks),  or  the  figure  may 
remain  practically  stationary  for  the  first  few  days,  and  then  a 
rise  set  in  until  a  constant  figure  is  arrived  at.  But  it  is  remark- 
able how  often  in  fresh  waters  no  evidence  is  to  be  obtained 
of  the  presence  of  the  intermediate  or  nitrite  stage  of  the  develop- 
ment of  nitrates;  and,  when  appreciable,  how  faint  the  evidence 
often  is.  In  polluted  sea  water,  however,  the  evidence  of 
oxidized  nitrogen  may  not  be  available;  for  under  ordinary 
conditions,  up  to  a  period  of  several  weeks,  no  oxidized  nitrogen 
may  appear  in  sea  water  as  the  result  of  sewage  contamination; 
but  it  ultimately  appears  in  amounts  which  give  very  definite 
reactions  by  qualitative  tests,  and  more  especially  is  this  true 
of  nitrites.  When  sewage  effluent  already  containing  nitrates 
and  nitrites  is  added  to  pure  sea  water  the  nitrates  disappear  in 
a  day  or  two,  though  a  trace  of  nitrites  may  persist  for  much 
longer.  Therefore,  as  nitrites  may  be  in  evidence  in  polluted 
sea  water  where  nitrates  are  not,  they  furnish  the  better  evidence 
of  sewage  contamination.  Thus  oxidized  nitrogen  in  sea  water 
will  indicate  contamination  which  is  either  very  recent  or  very 
remote;  but  its  absence  is  no  guarantee  of  freedom  from  such 
contamination  in  a  dangerous  form,  and  may  indeed  be  even 
more  significant  of  danger  than  its  presence  in  sea  water  which  is 
believed  to  have  been  recently  contaminated. 

Turning  next  to  the  free  and  albuminoid  ammonia  figures, 
which  form  such  a  useful  indication  of  animal  contamination  in 
fresh  waters.  When  small  proportions  (i  per  cent.)  of  sewage 
are  added  to  fresh  water,  there  is  to  be  noted  an  increase  of 
ammonia — generally  slight — for  the  first  few  days;  then  a 
reduction  sets  in,  and  after  several  days  or  several  weeks  (accord- 
ing to  season  and  dosage)  this  evidence  of  contamination  has 
disappeared.  When  sea  water  is  similarly  contaminated  a 
slight  preliminary  increase  is  to  be  noted  for  two  or  three  weeks, 


SEA   WATER  133 

and  then  reduction  generally  sets  in  slowly.  Therefore  the  free 
ammonia  figure  is  a  very  valuable  clue  to  contamination  of  sea 
water,  forming  invariably  an  item  of  evidence  which,  starting  at 
the  actual  time  of  contamination,  persists  for  several  weeks. 

When  small  proportions  of  sewage  are  added  to  fresh  water, 
an  increase  in  the  albuminoid  ammonia  figure  is  to  be  noted, 
which  often  persists  for  several  weeks,  so  that  the  figure  may 
reach  one  several  times  greater  than  the  original  figure;  then 
an  irregular  fall  sets  in  through  many  weeks.  But  in  ^ea  water 
we  find  that  the  preliminary  increase  is  less  rapid,  the  original 
figure  being  generally  found  after  two  or  three  weeks,  and  later 
there  is  some  reduction.  When  this  figure  in  pure  sea  waters 
is  compared  with  the  free  and  saline  ammonia  figure,  it  is  found 
that  not  only  is  it  always  a  much  higher  figure,  but  that  it  is 
subject  to  far  greater  variations.  With  these  more  indefinite 
characteristics  the  figure  does  not  lend  itself  as  a  basis  for  com- 
puting the  lesser  degrees  of  sewage  contamination. 

Pure  sea  water  has  a  considerable  reducing  action  upon 
potassium  permanganate  under  the  conditions  of  the  processes 
employed  in  water  analysis.  The  oxygen  absorbed  figure  in 
pure  sea  water  generally  approximates  to  0-5  part  per  100,000 
in  four  hours  at  the  temperature  of  the  laboratory,  and  careful 
analysis  may  furnish  no  appreciable  difference  when  sea  water 
is  polluted  with  i  per  cent,  of  sewage  effluent.  It  is  obvious, 
therefore,  that  this  process  does  not  assist  us  in  determining 
the  presence  of  the  lesser  degrees  of  contamination  of  sea  water. 

Nor  does  the  dissolved  oxygen  in  slightly  contaminated  sea 
water  furnish  reliable  results,  for  the  figure  falls  with  the  time 
which  has  elapsed  since  the  sample  was  taken ;  and  the  differences 
between  pure  sea  water  and  sea  water  contaminated  with  i  per 
cent,  of  sewage  effluent  are  often  so  slight  as  to  be  unserviceable. 

Phosphates  are  absent  from  pure  sea  water,  and  their  presence 
is  valuable  corroborative  evidence  of  contamination.  The  evi- 
dence, however,  may  be  obscure  where  the  contamination  is 
slight;  but  working  with  100  c.c.  of  sea  water,  the  ammonium 
molybdate  reaction  is  generally  appreciable  when  sea  water  is 
contaminated  with  quite  small  proportions  of  sewage. 

Interesting  and  suggestive  as  are  the  results  of  laboratory 
experiments  extending  over  many  weeks,  one  may  not  argue 
from  the  results  of  sewage  contamination  of  stationary  sea  water 
employed  in  experiments  to  sea  water  moving  under  the  in- 


134 


LABORATORY   WORK 


iluence  of  tides,  eddies,  and  currents.  To  keep  to  the  practical 
issues  of  the  problem  it  is  necessary  to  observe  the  behaviour  of 
sewage  contamination  during  a  period  of  at  most  several  days 
instead  of  several  weeks;  and  it  is  upon  these  considerations 
that  the  following  conclusions  upon  the  chemical  evidence  of 
slight  sewage  pollution  of  sea  water  are  based: 

We  may  conclude  that  the  free  and  saline  ammonia  figure 
furnishes  the  only  reliable  chemical  guide  to  the  lesser  degrees 
of  animal  contamination  of  sea  water;  that  delicate  corrobora- 
tive evidence  ma}'  sometimes  be  obtained  from  the  presence  of 
nitrites  and  phosphates;  but  the  complete  absence  of  oxidized 
nitrogen  is  compatible  with  recent  pollution,  and  it  is  not  always 
easy  to  obtain  a  definite  reaction  for  phosphates  when  the 
contamination  is  but  slight.  The  free  and  saline  ammonia 
figure  remains  of  all  the  available  tests  hitherto  suggested  the 
most  reliable  and  the  most  delicate;  and  an  ammonia  figure 
much  exceeding  0-002  part  per  100,000  is  certain  evidence  of 
the  sewage  contamination  of  sea  water. 

Samples  of  Pure  Sea  Water,  obtained  from  Points  at  which  the 
Water  was  judged  to  be  Free  from  Pollution:  (Parts  per 
100,000). 


Neighbourhood  where  Sample 

Free  and  Saline 

Albuminoid 

1 

Nitrogen  as 
Nitrates  and 

collected. 

Ammonia. 

Ammonia. 

Nitrites.* 

Aberdeen 

O'OOI 

0-007 

COO 

Bournemouth . 

o-ooi8 

0-002 

o-oo 

Carnarvon 

0'Ooi5 

0-006 

o-oo 

Clacton 

o-ooi 

0-004 

o-oo 

Folkestone 

0-002 

0-004 

o-oo 

Hastings 

0'00i5 

0-003 

o-oo 

Ilfracombe 

0'00i5 

0-0075 

o-oo 

Oban    .  . 

O-OOI 

o-oog 

o-oo 

1   Scarborough    . 

O-OOI 

0-005 

o-oo 

Ventnor 

O-OOI 

0-016 

o-oo 

There  is  also  available  the  method  of  taking  several  samples 
for  comparative  purposes  and  of  judging  the  presence  and  degree 
of  contamination  in  any  particular  sample  from  any  observed 
variations — more  particularly,  in  the  case  of  sea  water,  in  the 

*  Professors  E.  A.  Letts  and  E.  H.  Richards  find  that  a  trace  of  nitrates 
(averaging  0-005  N  per  100,000)  may  be  demonstrated  in  pure  sea  water, 
by  adding  to  25  c.c.  of  the  water  a  few  drops  of  brucine  sulphate  solution 
and  25  c.c.  of  strong  HgSOj. 


SEA   WATER  1 35 

ammonia  and  oxidized  nitrogen  figures.  Tin's  method  will  often 
be  serviceable,  and  should  always  be  availed  of  wlienever  it  is 
possible  to  obtain  fair  control  samples  from  situations  obviously 
more  remote  from  any  source  of  contamination. 

In  analyses  of  sea  water,  the  nitrates  should  be  tested  for, 
qualitatively,  by  brucine  and  sulphuric  acid,  and  the  nitrites 
by  Ilosvay's  method.  The  oxidized  nitrogen  should  be  esti- 
mated quantitatively  by  the  wet  copper-zinc-copper  process. 
The  oxidizable  organic  matter,  by  Tidy's  process,  conducted  at 
the  laboratory  temperature;  and  the  dissolved  oxygen  by 
Winkler's  process.  The  phosphates  should  be  tested  in  lOO  c.c. 
of  the  sample  by  first  adding  strong  nitric  acid,  and  then  evapor- 
ating to  a  solid  residue;  the  residue  to  be  then  digested  in  strong 
nitric  acid  and  the  filtrate  tested  with  molybdic  solution. 


CHAPTER  XVI 

ALKALIMETRY  AND  ACIDIMETRY— ICE— MINERAL  WATERS 
—ANALYTICAL  SCHEMES 

Alkalimetry  and  Acidimetry. 

For  the  purposes  of  estimating  the  degree  of  alkahnity  or  acidity 
of  water,  it  is  convenient  to  use  standard  solutions  based  upon 
the  atomic  or  molecular  weights  of  the  different  reagents;  or 
made  up  so  that  equal  volumes  of  the  solutions  are  chemically 
equivalent  to  each  other. 

Such  solutions  are  "normal"  when  they  contain  in  i  litre 
at  i6°  C.  chemically  equivalent  weights  of  the  active  reagents 
weighed  in  grammes,  hydrogen  being  taken  as  the  unit.  There- 
fore the  normal  solution  of  hydrochloric  acid  must  contain  the 
molecular  weight  of  the  acid — i.e.,  36-46,  in  grammes  per  litre, 
since  HCl  is  a  univalent  substance.  The  normal  solution  of 
sodium  carbonate  (NagCOs)  must  contain  the  molecular  weight 
of  the  salt  {(23  x  2) +12  +  16  x  3)}  divided  by  2=53  grammes 
per  litre;  for  the  molecule  of  monobasic  HCl  can  neutralize  only 
half  a  molecule  of  the  bivalent  NaaCOg. 

But  the  hydrogen  equivalent  of  some  reagents  is  not  so  easily 
arrived  at.  Take,  for  instance,  potassium  permanganate;  the 
molecular  weight  of  the  formula  (KoMuoOg)  is  316,  and  the  normal 
solution  is  31-6  grammes  per  litre.  This  is  because  316  grammes 
of  permanganate  of  potash  liberate  80  grammes  of  oxygen, 
which  are  chemically  equivalent  to  10  grammes  of  hydrogen; 
and  so  31  "6  grammes  of  the  salt  are  equivalent  to  i  gramme  of 

Hydrogen.  ^     ^^^^^  ^g^^ 

"  Seminormal  "  and  "  decinormal  "  solutions  are  obviously 
those  made  up  to  h  and  yV,  respectively,   of  the  strength   of 

136 


ALKALIMETRY    AND    ACTDIMETRY  137 

the  "  normal  "  solutions.  They  are  commonly  expressed  as 
^  and  J^f  solutions. 

Thus  each  c.c.  of  a  normal  solution  of  HCl  will  contain  j^Vo  o^ 
t he  molecular  weight  of  t he  acid  in  grammes  {i.e.,o- 03646  gramme) , 
and  each  c.c.  of  a  decinormal  solution  will  contain  0-003646 
gramme. 

Therefore  measured  quantities  of  normal  and  decinormal  acids 
should  exactly  neutralize  similar  quantities  of  the  normal  and 
decinormal  alkalies;  and  if,  on  titration,  they  are  not  found  to 
quite  correspond^  the  difference  must  be  ascertained  and  a  simple 
calculation  made  in  order  to  correct  it. 

In  estimating  alkalinity  the  decinormal  solution  of  hydro- 
chloric acid  may  conveniently  be  employed,  and  for  acidity  the 
decinormal  solution  of  sodium  carbonate.  In  either  case  one  of 
these  standard  solutions  would  have  to  be  added  in  measured 
quantity  until  the  neutral  stage  is  exactly  reached,  as  indicated 
by  a  suitable  reagent  which  is  added  to  the  solution. 

Methyl-orange  (about  i  gramme  to  the  litre)  is  a  good  "  indi- 
cator "  where  the  alkalinity  of  water  is  being  tested.  This  sub- 
stance has  the  property  of  yielding  a  beautiful  scarlet  colour  in 
the  presence  of  acidity;  but  its  solution,  which  is  of  a  bright 
orange  colour,  must  not  be  emplo3^ed  where  organic  acids  are 
concerned  or  where  nitrites  are  present.  In  these  cases  phenol- 
phthalein  may  be  substituted;  but  not  if  free  carbonic  acid  is 
present.  Phenolphthalein  dissolved  in  50  per  cent,  alcohol 
is  a  colourless  solution  which  strikes  a  rose-red  colour  in  the 
presence  of  alkalinity;  but  is  colourless  in  acid  solutions.  The 
marked  presence  of  ammonium  salts  would  vitiate  the  results 
when  phenolphthalein  is  employed.  Litmus  should  not  be  used 
as  an  "  indicator,"  for  the  COg,  so  commonly  present  in  water, 
considerably  masks  its  indications.  A  solution  of  cochineal  is 
almost  free  from  this  drawback,  and  is  a  useful  indicator;  it  is 
prepared  by  digesting  the  dried  and  powdered  cochineal  in  warm 
water  to  which  a  little  alcohol  has  been  added,  and  then  filtering; 
the  solution  has  a  yellow  or  yellowish-red  colour,  which  is  turned 
violet-red  by  alkalies,  and  the  original  colour  is  restored  by 
mineral  acids. 

A  I  per  cent,  solution  of  rosolic  acid  in  dilute  alcohol  is  a 
delicate  indicator.  Even  COg  and  acid  salts  change  the  indicator 
to  a  yellowish  tint,  the  colour  being  rose  in  alkaline  solu- 
tions. 


138  LABORATORY   WORK 

Example. — It  is  desired  to  estimate  the  alkalinity  of  a  water 
sample.  A  few  drops  of  the  methyl-orange  "  indicator  "  are 
added  to  100  c.c.  of  the  water  in  a  white  porcelain  dish.  A  deci- 
normal  (or  centinormal)  solution  of  HCl  is  then  dropped  in  from 
a  graduated  burette  until  evidence  of  a  scarlet  tint  appears, 
denoting  all  alkalinity  to  be  neutralized.  It  took  6  c.c.  of  the 
decinormal  acid  to  effect  neutrality,  therefore  the  alkalinity  is 
equivalent  to  6  c.c.  of  this  acid  solution.  But  6  c.c.  of  the 
decinormal  HCl  is  equivalent  to  a  similar  amount  of  deci- 
normal sodium  carbonate  solution;  therefore  the  alkalinity 
is  equivalent  to  6  c.c.  of  decinormal  sodium  carbonate  solu- 
tion. 

But  I  litre  of  the  normal  solution  contains  53  grammes  of 
sodium  carbonate,  therefore  i  litre  of  the  decinormal  solu- 
tion contains  5-3  grammes,  and  i  c.c.  of  this  contains  0'0053 
gramme,  and  6  c.c.  contain  0-0318  gramme  of  sodium 
carbonate. 

Therefore  the  alkalinity  of  100  c.c.  of  the  solution  is  equivalent 
to  0-0318  gramme  of  sodium  carbonate,  or  31-8  parts  of  sodium 
carbonate  per  100,000. 

In  estimating  the  aciditj'  of  a  peaty  water,  the  "  indicator  " 
— one  or  two  drops  of  an  alcoholic  solution  of  phenolphthalein — 
is  added,  and  the  sodium  carbonate  decinormal  solution  run  in 
until  a  very  faint  pink  tint  is  obtained,  when  the  calculation  is 
made  as  above. 

To  prepare  the  normal  HCl  it  is  necessary  to  take  about  181 
grammes  of  liquid  acid  of  the  S.G.  i-io,  and  dilute  to  a  litre  with 
water;  then  titrate  the  exact  strength  with  normal  sodium  car- 
bonate. 

Ice. 

Both  artificial  and  natural  ice  are  liable  to  furnish  on  analysis 
considerable  evidence  of  pollution,  which,  since  pathogenic 
organisms  can  survive  in  ice  for  long  periods,  must  be  regarded  as 
significant  of  danger.  Under  natural  conditions  the  most  super- 
ficial layer  of  the  ice  contains  most  impurity. 

The  popular  belief  that  water  purifies  itself  by  freezing  is 
unfounded.  It  is  certainly  not  borne  out  when  the  water 
obtained  from  the  melted  ice  is  subjected  to  chemical  analysis 
and  bacteriological  examination. 


MINERAL   WATERS  139 

The  results  of  many  analyses  performed  in  this  country, 
America  and  the  Continent,  show  the  following  variations: 

Parts  per  100,000. 

Free  and  saline  ammonia   .  .  . .     from  O'OOi  to  0'32 

Albuminoid  ammonia         ..  ..         ,,     0  "002  to  0*44 

Chlorine  as  chlorides  .  .  . .  ,,         o"i  to  6-5 

N  as  nitrates  .  .  .  .  .  .         ,,     nil  to  traces 

Total  solid  matter   .  .  . .  . .         ,,     i  to  50 

Bacteria  per  c.c,  40  to  2,000. 

Mineral  Waters. 

The  examination  of  mineral  waters  for  public  health  purposes 
should  be  conducted  on  precisely  the  same  lines  as  those  of  an 
ordinary  water  analysis;  that  is  to  say,  an  effort  must  be  made  to 
ascertain  the  freedom  of  the  water  from  dangerous  organic  and 
metallic  contamination. 

Artificial  mineral  "  waters  "  consist  of  water  into  which  car- 
bonic acid  is  forced  under  pressure.  Lithia  water  is,  in  addition, 
charged  with  lithia;  potass  water  with  bicarbonate  of  potash; 
soda  water  is  commonly  sold  without  the  addition  of  any  soda, 
but  when  such  is  added  it  is  usually  to  the  extent  of  about 
10  grains  of  bicarbonate  to  the  pint. 

Natural  mineral  waters  are  generally  the  purest.  Those  which 
are  chalybeate  mostly  contain  the  iron  in  the  form  of  ferrous 
carbonate,  held  in  solution  by  excess  of  carbonic  acid,  such  as 
those  at  Tunbridge  Wells,  Spa,  and  Cheltenham.  Instances  of 
alkaline  waters  naturally  charged  with  carbonic  acid,  and  con- 
taining sodium  carbonate  and  bicarbonate,  are  found  at  Carlsbad, 
Ems,  Malvern,  Nieder-Seltzers,  and  Vichy.  At  Harrogate  and 
Aix-la-Chapelle  waters  are  found  naturally  charged  with  sul- 
phuretted hydrogen.  Those  waters  which  possess  a  marked 
aperient  action  generally  owe  their  properties  to  either  sulphate 
of  magnesia,  as  at  Epsom  and  Leamington,  or  to  sulphate  of  soda, 
as  at  Cheltenham  and  Scarborough.  In  Central  Wales  there 
is  a  deep  spring  containing  9  parts  of  barium  chloride  per 
100,000. 

If  the  sample  is  collected  from  a  well  and  it  is  desired  to  know 
the  temperature  of  the  water,  the  thermometer  should  be  let  down 
in  a  stout  glass  bottle ;  this  will  come  up  fiUed  with  the  water. 


140  LABORATORY   WORK 

and  a  reading  of  the  thermometer  when  surrounded  by  the  water 
can  be  taken. 

All  artificial  mineral  waters  should  be  tested  for  lead,  iron, 
copper,  zinc,  and  arsenic.  Each  of  these  metals  has  been  found 
in  samples  of  soda  water,  etc.,  to  which  the  metal  has  gained 
access  either  by  the  apparatus  used,  the  improper  washing  of  the 
carbonic  acid,  or  from  the  use  of  metal  taps  to  the  syphons. 
Sometimes  a  considerable  quantity  of  lead  is  present  and  very 
impure  water  is  used;  on  this  account  it  is  desirable  that  efficient 
supervision  should  be  exercised  over  their  manufacture. 

Lemonade  and  ginger-beer  are  also  liable  to  contain  traces  of 
lead,  derived  from  the  apparatus,  and,  in  the  case  of  the  former, 
from  the  impure  tartaric  acid  emploj'ed. 

The  sediment  sometimes  yielded  by  mineral  waters  after  long 
storage  generally  consists  of  hydrated  ferric  oxide,  alumina,  silica, 
and  calcium  carbonate. 

The  carbonic  acid  of  aerated  waters  is  unfavourable  to  germ 
life,  and  the  bacteriological  counts  are  generally  low. 

In  aerated  waters  the  large  amount  of  carbonic  acid  inter- 
feres with  the  estimation  of  the  free  and  saline  ammonia  by 
Nesslerization,  and  must  therefore  be  remo\-ed  as  follows:  The 
ammonia  should  be  fixed  with  10  c.c.  of  normal  sulphuric  acid, 
then  the  water  is  heated  to  drive  off  the  carbonic  acid,  and  after 
neutralizing  the  acid  with  10  c.c.  of  normal  sodic  hydrate,  the 
ammonia  may  be  distilled  over  and  estimated. 

\\nien  it  is  found  necessary  so  to  deal  A\-ith  carbonic  acid,  a 
blank  experiment  should  be  performed,  in  which  any  ammonia 
found  in  500  c.c.  of  ammonia-free  distilled  water  containing 
10  c.c.  of  normal  sulphuric  acid  and  10  c.c.  of  normal  sodic 
hydrate  is  distilled  over  and  estimated,  and  this  is  deducted  in 
arriving  at  the  figure  of  the  free  and  saline  ammonia  in  the 
sample. 

Scheme  for  Effecting  an  Analysis  in  the  Quickest  and 
Most  Convenient  Manner. 

Although  a  little  confusion  may  be  experienced  at  first,  yet, 
after  a  little  practice,  the  following  plan  will  be  found  practical 
and  expedient,  the  time  required  being  about  three  hours. 

I.  Start  the  process  for  the  estimation  of  the  oxidizable  organic 
matter. 


ANALYTICAL    SCHEME  I4I 

2.  Start  the  evaporation  for  the  estimation  oi  the  total 
solids. 

3.  Start  the  concentration  of  the  water  for  the  purpose  of 
testing  for  poisonous  metals,  etc. 

4.  Start  the  distillation  for  the  estimation  of  the  free  and 
saline  ammonia. 

5.  Start  the  water  boihng  for  the  estimation  of  temporary  and 
permanent  hardness. 

6.  Start  the  alkaline  permanganate  boiling  in  preparation  for 
the  second  stage  of  Wanklyn's  process. 

7.  Apply  qualitative  tests  for  nitrates,  nitrites,  sulphates,  and 
phosphates. 

8.  Start  the  quantitative  estimation  of  oxidized  nitrogen 
(picric  acid  process). 

9.  Make  the  quantitative  estimation  of  chlorine. 

10.  Make  the  quantitative  estimation  of  total,  temporary,  and 
permanent  hardness. 

(By  this  stage  the  free  and  sahne  ammonia  will  be  over,  the 
alkahne  permanganate  may  be  added  to  the  boihng-fiask, 
and  the  distillation  for  the  albuminoid  ammonia  started.) 

11.  Estimate  the  free  ammonia. 

12.  Care  has  been  taken  throughout  not  to  disturb  any  deposit 
which  may  be  present.  Now  collect  and  make  an  examination 
of  any  sediment  or  suspended  matter.  Note  the  physical  char- 
acters in  the  2-feet  tube. 

13.  Estimate  the  albuminoid  ammonia. 

14.  Complete  the  picric  acid  process. 

15.  Estimate  the  oxygen  absorbed. 

16.  Test  for  poisonous  metals,  and  estimate  quantitatively  if 
any  one  is  present. 

17.  Complete  the  estimation  of  the  total,  volatile  and  non- 
volatile solids. 


PART    II 

SEWAGE  AND  SEWAGE  EFFLUENTS 

,«  collecting  samples  of  sewage  or  sewage  effluents  for  analyst 
the  average  sample  should  be  obtained  m  each  case.  This  may 
*  done  by  mix,ng  together  the  hourly  samples  taken  through- 
out the  day,  and  these  should  vary  m  bulk  m  proportion  to  the 
flow  of  sewage  or  effluent  at  the  tune  when  each  sample  is  taken, 
S::re,usingbottlesofonesi.eforcollectinga,lthe  sample. 

the  bottle  is  filled  if  the  maximum  flow  of  sewage  is  observed 
at  the  time  the  sample  is  taken;  if  half  the  maximum,  the 
bottle  is  half  ailed,  and  so  on.  When  aJl  these  samples  are 
mixed  together,  the  mixture  wiU  fairly  represent  the  average 
romposltTn;    akd   a  part    of    this    should  be  taken  for  the 

"itf  of  the  greatest  importance  that  the  an^ysis  should  be 
perfo  med  as  soon  after  the  collection  of  the  sample  as  possible 
'or  important  changes  may  be  rapidly  brought  about  by  the 
teer^ing  micro-organisms  present.  About  J  litre  is  he  amount 
reqS  for  a  complete  analysis.  The  bottle  should  be  quite 
S  with  the  sample  to  be  analyzed  and  i  more  than  a  day 
passes  before  the  analysis  is  undertaken  it  should  be  kept  in  a 
cold  chamber  in  the  interval. 

The  estimations  made  in  the  analysis  of  sewage  and  sewage 
effluents  include:  The  free  and  saline  ammoma  the  albuininoid 
ammonia,  the  chlorine,  the  oxidized  nitrogen,  the  to  al  -ohds  m 
soteion    volatile  and  non-volatile),  and  the  suspended  matter 
m  estimation  of  the  dissolved  oxygen  absorbed  by  an  effluent 
is  displacing  that  of  the  oxidizable  organic  matter  which  was 
fortriy  so'genetally  employed.     In  addition  so  '-  as  effluen 
are  concerned,  the  physical  characters  are  noted,  and  not  infre 
nuently  an  incubation  test  (at  about  27°  C)  is  applied,  m  order 
?o  seelf  the  sample  develops  odour  at  the  end  of  a  day  or  two. 


144  LABORATORY   WORK 

As  a  general  rule,  a  sample  of  effluent  is  allowed  to  deposit  before 
the  quantities  are  removed  for  analysis;  and  as  in  samples  of 
Sewage  the  matter  remaining  in  suspension  is  considerable  and 
leads  to  variable  analytical  results,  two  or  more  analj^ses  should 
be  performed  of  the  sample,  and  the  mean  taken  of  the  different 
figures  obtained;  and  the  solids  maj^be  estimated  both  before  and 
after  the  sample  has  been  shaken,  and  the  two  results  given. 

The  results  of  the  anah-sis  should  be  expressed  in  terms  of 
parts  per  100,000  to  the  second  place  of  decimals;  analyses  which 
record  a  third  or  fourth  place  of  decimals  give  a  fictitious  ap- 
pearance of  accurac}^  when  such  a  changeable  substance  as 
sewage  or  as  sewage  effluent  is  concerned. 

The  anah-sis  proceeds  upon  similar  lines  to  those  of  water 
analj-sis,  but  it  is  necessary  to  dilute  the  sewage  matter  to  a 
considerable  extent  before  commencing  certain  of  the  estima- 
tions.    So  far  as  the  solids  are  concerned,  these  may  be  estimated 
from  the  original  sewage  or  effluent,  but  for  the  calculation  of 
the  two  ammonias  20  c.c.  of  sewage  effluent  and  10  c.c.  of  sewage 
should  be  made  up  to  the  litre  with  ammonia-free  distilled  water, 
and  the  results  obtained  will  represent  the  amounts  in  20  c.c.  and 
10  c.c.  respectivel^^     In  Nesslerizing  the  ammonias  the  contents 
of  the  Nessler  glasses  may  be  all  mixed  together  in  a  beaker,  and 
the  colour  of  50  c.c.  matched;  thus,  supposing  200  c.c.  of  the 
distillate  were  collected  before  all  the  free  "  ammonia  "  had  come 
over,  then  the  ammonia  estimate  in  50  c.c.  must  be  multiplied 
by  4.     For  Tidj^'s  process  20  c.c.  of  effluent  and  10  c.c.  of  sewage 
should  be  added  to  100  c.c.  of  distilled  water.   The  nitrates  may 
be  estimated  from  the  original  effluent  by  the  phenol-sulphonic 
acid  method.  For  the  estimation  of  the  chlorine  the  effluent  should 
generally  be  first  diluted  with  an  equal  quantity  of  distilled  water. 
The  amount  of  chlorine  is  practically  unaffected  by  the  usual 
methods  of  sewage  purification,  and  if  its  quantity  is  not  added 
to  by  the  w^aste  liquors  from  manufacturing  processes  (ferrous 
chloride — iron  pickle,  or  salt)  it  furnishes  a  useful  clue  to  the 
strength  of  the  original  sewage.     About  10  parts  per  100,000 
may  be  taken  to   indicate   sewage  of   average  strength.     It  is 
generally  necessary  to  fflter  the  sewage,    and  occasionally  the 
effluent,  before  making  this  quantitative  estimation. 

In  performing  Tidy's  process  it  will  often  be  noted  that  the 
solution  becomes  decolorized  at  the  bottom  first.  The  flask 
should,  therefore,  be  shaken  from  time  to  time.     Various  coal- 


sewaCxp:  and  si<:wage  effluents  145 

tar  products,  indigo,  logwood  and  other  dyes,  and  such  salts  as 
thiocyanates,  sulphites  and  sulphides,  will  also  absorb  oxygen  in 
addition  to  oxidizable  organic  matter. 

In  performing  Wanklyn's  process,  if  the  ammonias  come  over 
very  slowly,  so  that  the  water  in  the  boiling-flask  reaches  below 
150  c.c,  then  a  further  100  c.c.  of  ammonia-free  distilled  water 
should  be  added  to  the  boiling-flask.  In  the  case  of  sewage  or 
bad  effluents  it  is  sometimes  difficult  to  get  all  the  albuminoid 
ammonia  over  without  adopting  this  expedient. 

In  the  estimation  of  N  as  nitrates  the  picric  acid  process  is  to 
be  preferred,  but  this  method  may  yield  unsatisfactory  results 
if  the  effluent  contains  waste  gas  liquors.  In  such  a  case  the 
effluent  should  be  diluted,  and  the  wet  copper-zinc  couple  method 
employed. 

The  amount  of  suspended  matter  will  indicate  the  amount  of 
deposit  hkely  to  take  place  in  a  stream.  It  may  be  estimated 
with  sufficient  accuracy  by  collecting  it  from  500  c.c.  of  effluent 
or  100  c.c.  of  sewage,  on  previously  well-washed,  dried,  and 
weighed  fine  hard  filter-papers. 

The  albuminoid  ammonia  figure  is  a  fair  indication  of  the 
amount  of  organic  matter,  but  the  organic  nitrogen,  as  estimated 
on  Kjeldahl's  principle,  is  a  much  more  inclusive  estimation  than 
the  albuminoid  ammonia,  and  it  is  almost  as  easily  arrived  at 
Although  it  will  be  found  that  the  organic  nitrogen  of  Kjeldahl's 
process  averages  a  little  over  twice  the  nitrogen  of  the  albu- 
minoid ammonia  (though  sometimes  showing  marked  departures 
from  this  average),  the  fact  that  the  two  analytical  figures  do  not 
bear  a  constant  ratio  to  one  another  is  significant,  and  points  to 
the  desirability  of  adopting  the  more  inclusive  estimation. 

The  presence  of  oxidized  nitrogen  in  an  effluent  must  not  be 
regarded  as  insuring  absence  of  odour,  although  if  nitrates  are 
found  to  persist  in  an  inoffensive  effluent  for  a  few  days  after  its 
collection,  the  effluent  is  not  likely  to  become  offensive.  Nitrates 
are  a  measure  not  of  that  poUution  which  may  be  oxidized,  but 
of  that  which  has  been  oxidized,  and  their  presence  often  gives 
little  indication  of  what  remains  to  be  purified;  but  generally 
high  nitrates  are  a  good  feature  in  a  sewage  effluent. 


146  laboratory  work 

Organic  Nitrogen  by  Kjeldahl's  Method  (Modified). 

I., Place  20  c.c.  of  the  sewage  or  sewage  effluent  into  a  small 
flask,  and  after  adding  about  i  c.c.  of  sulphuric  acid  evaporate 
over  the  water-bath  to  about  5  c.c. 

2.  Add  20  c.c.  of  pure  concentrated  H2SO4,  close  the  mouth 
of  the  flask  by  a  small  glass  funnel,  and  boil  slowly  for  an  hour 
or  two  until  the  solution  is  of  a  clear,  pale  yellow  colour. 

3.  Let  cool,  and  then  transfer  the  contents  of  the  small 
flask  to  a  distilling  flask,  being  careful  to  well  wash  out  the 
small  flask  and  to  transfer  the  washings  to  the  distilling 
flask. 

4.  Make  up  the  bulk  of  liquid  to  about  500  c.c.  with  ammonia- 
free  distilled  water,  and  then  neutralize  the  acid  with  excess  of 
strong  potassic  hydrate  solution.  The  amount  necessary  to  add 
can  be  determined  by  previously  ascertaining  how  much  is 
required  to  neutrahze,  sa3^  22  c.c.  of  the  concentrated  acid  in 
water. 

5.  Heat  a  piece  of  pumice-stone  to  bright  redness,  and  drop 
it  into  the  flask  to  prevent  "  bumping."  Distil  over  about 
400  c.c,  receiving  the  first  portion  of  the  distillate  into  a  flask 
containing  20  c.c.  of  ammonia-free  water  slightly  acidulated  with 
two  drops  of  dilute  sulphuric  acid,  the  distillate  being  received 
direct  into  this  solution. 

6.  Nesslerize  the  ammonia;  and  [i  of  this  will  be  nitrogen. 

7.  Deduct  the  amount  of  nitrogen  as  "  free  and  saline  am- 
monia "  in  20  c.c.  of  the  original  sewage  or  effluent  (previously 
ascertained  by  Wanklyn's  process)  and  the  difference  =  the  organic 
nitrogen.     Calculate  to  parts  per  100,000. 

8.  Always  make  a  blank  experiment  to  determine  the  amount 
of  ammonia  thus  obtained  from  the  reagents  and  distilled  water 
emploj^ed,  and  deduct  this  amount. 

Note. — By  the  action  of  the  sulphuric  acid  the  nitrogen  of  the 
organic  matter  is  converted  into  sulphate  of  ammonia.  The 
potassic  hydrate  liberates  the  ammonia,  which  is  then  distilled 
over. 

The  above  is  a  simple  method  of  estimating  the  organic 
nitrogen,  giving  results  which  vary  but  little  from  those  obtained 
from  working  with  the  solid  matter  of  a  litre  of  water.  In  the 
latter  case  a  few  grains  of  yellow  mercuric  oxide  and  of  potassium 
sulphate  should  be  added  to  the  solids  along  with  the  sulphuric 


STANDARDS    OF    PURITY    OF    SEWAGE    EFFLUENTS        I47 

acid,    and,    before   distillation,    50    c.c.    of   potassium    sulphide 
solution  (40  grammes  to  the  litre)  should  also  be  added. 

The  composition  of  sewage  from  the  same  district  varies  very 
greatly  from  time  to  time,  and  this  is  true,  though  to  a  less 
extent,  of  the  effluent.  The  effluent,  moreover,  varies  according 
to  the  method  and  degree  of  treatment ;  but  the  following  mean 
results  of  many  analyses  will  serve  to  give  the  reader  a  general 
idea  of  the  composition  of  domestic  sewage  and  sewage  effluents: 


Free  and  saline  ammonia 

Organic  ammonia     .  . 

O  absorbed  in  two  hours  at  27°  C. 

Nitrogen  as  nitrates  and  nitrites 

Chlorine 

Suspended  matter    . . 

Solids  in  solution 

(a)  Volatile 

(6)   Non-volatile 


Sewage  as  it  leaves  the 
Outfall  Sewer. 


Parts  per  100,000. 

6-5 
1-4 
9-6 

CO 

ii-i 
50 
90 
50 

40 


Effluent  after  the 
.Sewage  has  been 
chemically  treated 

and  then  passed 
through  Filter-beds. 
Parts  per  100,000. 
1-50 

0'i4 
1-35 

I'20 

IO-5 

2'0 

75 
32 
43 


Often  it  is  desired  to  obtain  an  expression  of  the  amount  of 
purification  obtained  by  a  given  method  of  treatment ;  it  is  then 
usual  to  calculate  the  percentage  amounts  of  purification  effected 
from  the  differences  between  the  "  albuminoid  ammonia  "  and 
"  oxygen  absorbed  "  figures  of  the  original  sewage  and  those  of 
the  effluent.  For  this  purpose  the  figures  of  the  original  sewage 
are  taken  as  100. 

Example. — ^The  albuminoid  ammonia  of  the  original  sewage  = 
0-8  part  per  100,000,  and  that  of  the  purified  effluent  =  0-2.     The 

percentage  purification  would  therefore  be — ^ =75- 


Standards  of  Purity  of  Sewage  Effluents. 

A  satisfactory  sewage  effluent  must  be  without  faecal  odour, 
and  should  possess  little  colour  or  turbidity.  It  has  been  sug- 
gested that  pearl  type  should  be  readable  through  a  column  of 
effluent  10  inches  in  depth.  In  parts  per  100,000  the  figure  of 
albuminoid  ammonia  should  not  exceed  o-i  or  0-15,  nor  the 
oxygen  absorbed  by  oxidizable  organic  matter  in  two  hours  at 
27°  C.  a  figure  of  1-5.      The  final  effiuent  must  not  be  liable  to 


148  LABORATORY   WORK 

putrefaction  or  secondary  decomposition;  and,  if  satisfactor}^ 
all  frothing  will  disappear  in  tlu-ee  seconds  after  a  half-lilled 
bottle  is  shaken  vigorously  for  one  minute. 

The  Royal  Commission  on  Sewage  Disposal,  appointed  in  1898, 
found  as  follows: 

The  harm  caused  b}^  allowing  unpurified,  or  imperfectly 
purified,  sewage  to  flow  into  rivers  and  streams  may  be  placed 
under  one  or  more  of  the  following  headings:  The  de-aeration 
of  the  water  of  the  river,  and  consequent  injury  to  fish;  the 
putrefaction  of  organic  matter  in  the  river  to  such  an  extent  as 
to  cause  nuisance;  the  production  of  sewage  fungus  and  other 
objectionable  growths;  the  deposition  of  suspended  matter,  and 
its  accumulation  in  the  river-bed  or  behind  weirs,  which  will 
draw  upon  the  oxygen  in  the  supernatant  water;  the  discharge 
into  the  river  of  substances,  in  solution  or  suspension,  which  are 
poisonous  to  fish  or  to  live-stock  drinking  from  the  stream;  the 
discoloration  of  the  river;  and  the  discharge  into  the  river  of 
micro-organisms  of  intestinal  derivation,  some  of  which  are  of  a 
kind  liable,  under  certain  circumstances,  to  give  rise  to  disease. 
The  extent  to  which  the  purification  of  a  sewage  need  be  carried 
varies  with  the  particular  circumstances  of  the  town  and  river 
concerned,  and  they  recommend  that  local  circumstances  should 
be  taken  into  account.  The  effect  of  an  effluent  on  a  stream 
does  not  generally  depend  on  the  absolute  amount  of  organic 
matter  contained  in  it,  but  rather  on  the  nature  and  condition 
of  that  organic  matter;  and  the  important  thing  to  ascertain 
in  examining  an  effluent  is  the  extent  to  which  the  contained 
organic  matter  has  undergone  fermentation. 

In  the  Eighth  Report  of  the  Royal  Commission  on  Sewage 
Disposal  the  Commissioners  deal  with  the  question  of  the  stan- 
dards to  be  applied  to  sewage  and  sewage  effluents  discharging 
into  rivers  and  streams,  and  the  test  which,  in  their  opinion, 
should  be  used  in  determining  those  standards.  The  Commis- 
sioners reiterate  a  previous  recommendation  that  Local  Authori- 
ties should  not  be  required  to  purify  their  sewage  more  highly 
than  is  necessary  to  obviate  the  risk  of  actual  nuisance  (from 
odour,  growths,  putrefying  solids,  and  detriment  to  fish  life) 
arising  from  its  discharge.  They  express  the  view  that  an 
effluent  ought  not  to  be  considered  alone,  but  that  the  nature 
and  volume  of  the  recipient  waters  should  always  be  taken  into 
consideration ;  and  that  any  standard  laid  down  ma}-  be  either  a 


STANDARDS   OF   PURITY   OF   SEWAGE   EFFLUENTS       I49 

general  standard  or  a  special  standard  which  will  be  higher  or 
lower  than  the  general  standard,  as  local  circumstances  require 
or  permit.  They  find  that  the  nuisance-producing  power  of  an 
effluent  is  broadly  proportional  to  its  deoxygenating  power  on 
the  stream;  and  it  is  recommended  that  an  effluent,  in  order  to 
comply  with  the  general  standard,  should  not  be  permitted 
to  contain  more  than  3  parts  per  100,000  of  suspended 
matter,  nor  with  the  suspended  matters  included  should  the 
effluent  take  up  more  than  2  parts  per  100,000  of  dissolved 
oxygen  in  five  days  when  it  is  maintained  at  a  temperature  of 
18°  C. 
The  Commissioners  classify  rivers  as  follows: 

"  Very  clean  "  if  no  more  than  o-i  part  of  oxygen  is  absorbed. 
"  Clean  "  if  no  more  than  0-2  part  of  oxygen  is  absorbed. 
"  Fairly  clean  "  if  no  more  than  0-3  part  of  oxygen  is  absorbed. 
"  Doubtful  "  if  no  more  than  0-5  part  of  oxygen  is  absorbed. 
"  Bad  "  if  more  than  i-o  part  of  oxygen  is  absorbed. 

The  above  figures  represent  the  parts  of  dissolved  oxygen 
taken  up  by  100,000  parts  of  the  water  in  five  days  at  18°  C. 

"  If  100,000  c.c.  of  river  water  (containing  effluent)  do  not 
take  up  more  than  0-4  gramme  of  dissolved  oxygen  in  five  days, 
the  river  will  ordinarily  be  free  from  signs  of  pollution,  but  above 
this  figure  it  wih  almost  certainly  show  them";  and  "if  the 
mixture  should  yield  a  figure  exceeding  0-4,  then  the  effluent 
would  have  to  be  improved."  "  This  figure  (0-4)  we  term  the 
'  limiting  '  figure,  and  in  our  opinion  it  should  be  the  foundation 
upon  which  any  scheme  or  standard  should  be  constructed  in 
order  to  ascertain  the  minimum  degree  of  purification  which 
would  be  sufficient  to  obviate  risk  of  nuisance." 

The  albuminoid  ammonia  and  acid  permanganate  tests  only 
yield  empirical  results  which  do  not  sufficiently  indicate  the  con- 
sequences which  follow  when  effluents  are  discharged  into 
streams;  acid  permanganate  is  too  vigorous  an  oxidizing  agent; 
and  the  amount  of  dissolved  oxygen  taken  up  from  water  by 
an  effluent  is  doubtless  a  test  which  possesses  an  advantage  as 
an  indication  of  what  naturally  takes  place. 

In  the  experience  of  the  Commissioners,  if  the  dilution  of  the 
effluent,  while  not  falling  below  150  volumes,  does  not  exceed 
300,  the  dissolved  oxygen  absorption  test  may  be  omitted,  and 
the  standard  for  suspended  solids  fixed  at  6  parts  per  100,000. 


150 


LABORATORY   WORK 


When  the  dilution,  while  not  falling  below  300  volumes,  does 
not  exceed  500,  the  standard  for  suspended  solids  may  be  further 
relaxed  to  15  parts  per  100,000.  Lastly,  with  a  dilution  of  over 
500  volumes,  the  Commissioners  conclude  that  all  tests  ma}'  be 
dispensed  with  and  crude  sewage  discharged,  subject  to  such 
conditions  as  to  the  provision  of  screens  or  detritus  tanks  as 
may  appear  necessary  to  a  Central  Authority.  It  is  not  possible, 
nor  is  it  necessary,  to  laj^  down  fixed  standards  with  reference  to 
tidal  waters. 

Some  effluents,  especiall}^  those  containing  iron  salts,  while 
free  from  visible  suspended  solids  at  the  time  of  sampling,  are 
capable  of  yielding  considerable  deposits  on  standing.  There- 
fore, as  suspended  matter  is  liable  to  separate  out  of  true  and 


FIG.    iS. APPARATUS    FOR    ADENEY'S    PROCESS. 

colloidal  solution  on  standing,  anj^  delay  in  making  the  estima- 
tion is  important.  Furthermore,  by  delay,  the  suspended  matter 
may  lead  to  a  material  reduction  of  the  oxygen  in  the  effluent. 

To  determine  the  amount  of  oxygen  which  a  sewage  effluent 
will  absorb  in  a  given  time,  a  definite  quantity  of  the  effluent  is 
allowed  to  remain  in  contact  either  with  atmospheric  air  or  with 
water  containing  a  high  figure  of  dissolved  oxygen.  For  the 
former  test  the  following  method  is  satisfactory  : 

Adeney's  Method  for  the  Determination  of  the  Rate  of  Absorption 
of  Dissolved  Oxygen  in  Polluted  Waters. — A  known  volume  of 
the  effluent  or  polluted  water — 100  to  250  c.c,  according  to  its 
strength — is  decanted  into  the  bottle  B,  into  which  a  little  freshly 
precipitated  magnesium  hydrate  has  been  previously  added  for 


SEWAGE   AND    SEWAGE    EFFLUENTS  15^ 

the  purpose  of  fixing  the  carbonic  acid  in  the  water.  A  similar 
volume  of  the  distilled  water  is  poured  into  the  bottle  A.  Similar 
volumes  of  air  will  thus  have  been  left  in  the  two  bottles.  The 
corks  with  the  connecting  tube  and  stopcocks  in  position  arc 
then  fitted  into  their  respective  bottles,  care  being  taken  pre- 
viously to  open  both  stopcocks.  A  slight  rise  of  water  from 
capillary  action  will  of  course  occur  in  the  portion  of  the  con- 
necting tube  in  the  bottle  A;  the  height  to  which  it  rises  in  this 
way  should  have  been  previously  marked  by  a  writing  diamond. 
This  mark  serves  as  an  index  for  subsequent  measurement.  The 
two  bottles  so  connected,  and  both  stopcocks  being  still  open, 
are  completely  immersed  in  the  water-bath  for  a  few  minutes  to 
allow  of  their  contents  assuming  a  common  temperature.  Both 
stopcocks  are  then  closed,  and  at  the  same  time  the  temperature 
of  the  bath  and  the  height  of  the  barometer  are  noted.  The 
apparatus  is  taken  out  of  the  water-bath  and  dried,  especiaUy  the 
corks,  which  when  completely  dry  are  coated  with  shellac  varnish 
to  prevent  diffusion  of  air  through  them.  It  is  then  put  into  a 
mechanical  shaker,  by  means  of  which  the  contents  of  the  two 
bottles  are  kept  in  gentle  motion. 

As  oxygen  is  absorbed  by  the  polluted  water  from  the  atmo- 
sphere in  B,  the  pressure  of  the  atmosphere  wih  be  reduced 
relatively  to  that  of  the  atmosphere  in  A,  which  will  be  unaffected 
by  the  distilled  water.  Consequently,  the  water  from  A  wiU  rise 
in  the  connecting  tube  b  in  proportion  to  the  volume  of  oxygen 
■absorbed  by  the  polluted  water  from  the  atmosphere  in  B.  ^  The 
volume  of  oxygen  which  is  indicated  by  the  rise  of  the  water  in  the 
connecting  tube  can  be  measured  at  any  time  by  attaching,  by 
means  of  a  flexible  tube,  a  burette  containing  distihed  water  at 
the  temperature  of  the  laboratory.  As  the  water  from  the  burette 
is  cautiously  allowed  to  flow  into  B,  the  water  in  the  connecting 
tube  wiU  gradually  sink  back  to  the  index,  when  the  stopcock  to 
the  bottle  B  is  closed;  and  the  volume  of  water  which  has  flowed 
from  the  burette  is  equal  to  the  volume  of  oxygen  which  has  been 
absorbed  from  the  atmosphere  of  B  at  the  temperature  and 
pressure  of  the  atmosphere  obtaining  at  the  commencement  of 
the  experiment.  It  may  here  be  noted  that  the  distilled-water 
bottle  A  acts  as  a  reference  pressure  bottle. 

If  a  comparatively  rapid  absorption  of  oxygen  occurs  during 
the  first  hour  or  two,  and  this  is  followed  by  a  slower  and  regular 
absorption,  it  may  safely  be  taken  to  be  due  to  the  poUuted  water 


152  LABORATORY  WORK 

being  de-aerated  to  start  with,  and  possibly  also  to  the  presence  of 
easily  and  directly  oxidizable  substances  in  it;  the  subsequent 
slower  and  regular  absorption  being  due  to  indirect  oxidation 
accompan}'ing  the  fermentation  of  the  polluting  matters. 

This  apparatus  may  also  be  employed  for  determining  the 
strength  of  a  crude  sewage  or  of  any  other  polluted  water  in  the 
crude  state,  after  the  solids  in  suspension  have  been  separated. 
The  sewage  should,  liowever,  be  diluted  with  four  to  nine  N'olumes 
of  tap  water. 

The  errors  affecting  the  estimation  are  negligible,  provided  care 
be  taken  at  the  commencement  that  the  \\'ater  and  air  in  the  two 
bottles  are  at  a  common  temperature  and  that  the  apparatus  is 
airtight  in  all  parts. 

Under  many  conditions  of  work  it  will  be  found  preferable  to 
employ  some  of  the  polluted  water  to  be  examined  instead  of  dis- 
tilled water  for  use  in  the  reference  pressure  bottle  A,  after  steril- 
izing it  by  the  addition  of  a  few  drops  of  a  concentrated  solution 
of  mercuric  cliloride  and  shaking  it  with  air  in  order  to  thoroughly 
aerate  it. 

It  is  sometimes  advantageous  that  the  bottles  employed  should 
be  larger  than  those  indicated  in  the  diagram,  and  should  be  of 
about  1,000  c.c.  capacity. 

The  Dissolved  Oxygen  Absorbed  in  Five  Days. 

The  method  adopted  by  the  Royal  Commission  for  this  deter- 
mination is  that  of  Winkler,  as  modified  by  Rideal  and  Stewart, 
the  particulars  of  which  are  as  follows: 

Reagents  required  : 

1.  Concentrated  sulphuric  acid. 

2.  Concentrated  hydrochloric  acid  (free  from  chlorine). 

3.  ^  permanganate  (3*94  grammes  KMNO4  per  litre). 

4.  Potassium  oxalate  (2  per  cent,  of  the  crystallized  salt). 

5.  Manganous  chloride  (33  per  cent,  of  the  crystallized  salt). 

6.  A  mixed  solution  of  caustic  potash  and  iodide  of  potassium,  containing 
70  grammes  KOH  and  10  grammes  KI  per  100  c.c. 

7.  Sodium  thiosulphate  solution,  containing  about  12  grammes  of  the 
salt  per  litre. 

The  Process. 
I.  Well  shake  the  effluent,  in  order  to  bring  its  dissolved  oxygen 
content  to  something  near  that  of  the  diluting  water;  wait  a  few 
minutes,  and  then  measure  300  c.c.  and  gently  mix  with  four 


SEWAGE    AND    SEWAGE    EFFLUENTS  153 

times  its  volume  of  well-aerated  tap  water  at  i8°  C.  (This  water 
will  contain  in  solution  about  7  c.c.  of  oxygen  per  litre,  or  i  part 
by  weight  of  oxygen  per  100,000  of  watei.) 

2.  Quietly  and  quickly  fill  four  small  bottles  (capacity  340  or 
360  c.c.)  with  this  mixture,  the  bottles  being  allowed  to  stand 
full  to  the  mouth  for  five  minutes,  and  then  stoppered. 

3.  Place  two  of  the  bottles  in  an  incubator  at  18"  C.  for  five 
days. 

4.  Determine  at  once  the  dissolved  oxygen  in  the  water  of 
the  other  two  bottles,  as  follows: 

{a)  First  add  o-g  c.c.  of  sulphuric  acid  and  then  sufficient  of  the  per- 
manganate to  still  provide  a  pink  colour  after  twenty  minutes. 
I  to  2  c.c.  of  |-  permanganate  are  generally  sufficient  for  this 
purpose.     Mix  the  contents,  and  let  stand  for  twenty  minutes. 

[b)  Remove  the  excess  of  permanganate  by  the  addition  of  about  i  c.c. 

of  the  oxalate  solution ;  restopper  and  mix. 

(c)  When  the  liquid  has  become  colourless,*  i  c.c.  of  manganous  chloride 

solution  is  run  into  the  bottom  of  the  bottle,  followed  imme- 
diately afterward  by  4  c.c.  of  the  solution  containing  potassium 
hydrate  and  potassium  iodide. 

{d)  Insert  stopper,  and  turn  over  the  bottle  once  or  twice;  let  stand  for 
a  few  minutes;  again  turn  over  once  or  twice,  and  then  allow 
the  hydroxides  of  manganese  to  settle. 

{e)  Add  5  c.c.  of  the  hydrochloric  acid,  restopper  and  let  bottle  stand 
in  shade  for  five  to  ten  minutes,  with  occasional  rotations. 

(/)  Twenty  c.c.  of  the  liquid  are  now  pipetted  out  and  rejected,  and  the 
remainder  is  titrated  with  thiosulphate,  as  described  on  p.  88. 

{g)  The  second  bottle  is  treated  in  the  same  way,  and  the  mean  of  the 
two  results  is  taken. 

{h)  At  the  end  of  five  days  the  dissolved  oxygen  in  the  incubated  bottles 
is  determined,  and  the  mean  of  the  two  results  is  subtracted  from 
the  first  mean.  The  difference  multiphed  by  5  gives  the  amount 
of  dissolved  oxygen  absorbed  by  100,000  parts  of  the  effluent 
in  five  days. 

Example  :  The  dissolved  oxygen  in  the  mixhtre  at  the  start.  The 
capacity  of  the  bottle=34i  c.c;  subtract  20  c.c;  and  volume 
of  mixture  tested=32i  c.c.  The  thiosulphate  used=6-95  c.c; 
but  each  c.c.  =  0-0003773  gramme  oxygen;  .-.  6-95  c.c.  =  0-0003773 
X  6-95  grammes  of  oxygen;  and  the  dissolved  oxygen  in  parts  per 

,  .         ,  0-0003773x6-95X100,000  ^.Q^„ 

100,000  of  mixture= ^^^-^^ ^^ =  0"bi7. 

321 

*  In  the  case  of  poor  effluents  and  tank  liquors  a  bro^^^l  precipitate  may 
form,  and  this  must  be  given  time  to  disappear. 


154  LABORATORY   WORK 

The  dissolved  oxygen  in  the  mixture  at  the  end  of  incubation 
similarly  calculated  =0-488  part  per  100,000. 

Thus  0-817- 0-488  =  0-329  gramme  of  dissolved  oxygen  is 
taken  up  by  100,000  parts  of  the  mixture;  and  as  1  of  this  mixture 
is  effluent,  0-329  x  5=  1-65  is  the  absorption  of  dissolved  oxygen 
by  100,000  parts  of  effluent  in  five  days  at  18°  C. 

Notes. — It  is  recommended  that  all  samples  should  be  allowed 
to  stand  at  18°  C.  for  forty-eight  hours  after  sampling  and  before 
carrying  out  the  test ;  and  if  it  is  not  possible  to  commence  the 
tests  at  the  end  of  that  time  the  sample  should  be  meanwhile 
kept  on  ice. 

For  practical  purposes  no  corrections  are  necessary  for  the 
few  c.c.  of  added  reagents. 

The  temperature  of  18°  C.  (65°  F.)  represents  the  maximum 
temperature  likely  to  be  reached  in  river  water.  The  tempera- 
ture of  the  incubator  should  not  var}^  more  than  one  degree  on 
either  side  of  this  standard  temperature. 

A  few  control  determinations  with  tap  water  alone  should  be 
done  from  time  to  time,  to  make  sure  that  the  tap  water  itself 
does  not  take  up  any  appreciable  quantity  of  oxygen. 

Effluents  conforming  to  a  satisfactory  standard  may  cause 
considerable  growths  of  organic  life,  which  may  subsequently 
produce  a  nuisance.  There  is  much  to  learn  of  the  causation  of 
these  objectionable  growths,  but  certain  of  them  are  doubtless 
promoted  by  the  presence  of  nitrates.  Carchesium  (constituting 
whitish  masses  of  fflamentous  growth,  characterized  by  bell- 
shaped  heads  on  thread-like  stems),  green  growths  of  Oscillatoria 
nigra  and  Spirogyra,  and  coarser  growths  of  water-weeds  may 
grow  in  well-purified  effluents ;  and  imperfectly  purified  effluents 
may  foster  such  grey  growths  as  Leptoniitus  and  Sphcerotilus, 
or  even  Beggiatoa. 

A  large  thin-leaf  seaweed,  of  cabbage-green  colour  and  known 
as  sea-lettuce  {Ulva  latissima),  like  different  species  of  the  grass- 
like Enteromorpha,  etc.,  flourishes  in  association  with  the  sewage 
pollution  of  sea  water.  The  ulva  grows  most  extensively  in  those 
estuaries  where  the  water  is  shallow  and  the  tidal  movements  are 
slow  and  ineffectual  in  carrying  all  the  sewage  pollution  out  to 
sea  at  each  ebb  of  the  tide.  We  are  indebted  to  Professor  E.  H. 
Letts  for  much  information  with  reference  to  this  sewage  seaweed. 
He  finds  that  it  absorbs  nitrogen  from  the  ammonia  and  nitrates 
of  sewage  origin,  and  that  mussels  attach  themselves  to  it  by 


SEWAGE-POLLUTED    MUD  155 

their  byssus  threads.  After  the  ulva  reaches  a  certain  size, 
wave  action  detaches  most  of  it,  and  the  small  retained  pieces 
are  capable  of  continuing  the  growth  of  the  plant.  If  the 
detached  ulva  is  not  swept  out  to  sea,  it  accumulates  on  the  shore, 
where,  exposed  to  the  sun  and  air,  fermentative  decomposition 
sets  in,  and  a  micro-organism  reduces  the  sulphates  (which  are 
abundantly  present  in  the  tissues  of  the  ulva)  to  sulphides;  and 
eventually  sulphuretted  hydrogen  is  liberated  and  an  intolerable 
nuisance  results. 

The  weed  is  also  found  in  some  places  where  the  sea  water  is 
free  from  sewage  pollution,  in  sheltered  and  shallow  waters  with 
sluggish  currents,  and  where  the  means  for  its  anchorage  exist. 

In  sewage-polluted  mud  the  N  could  be  determined  in  lo 
grammes  of  the  mud  by  the  Kjeldahl  method.  Information  may 
also  be  obtained  as  regards  the  deoxygenating  qualities  of  the 
mud  deposited  in  the  bed  of  a  stream.  Twenty-five  grammes  of 
the  mud  should  be  mixed  with  500  c.c.  of  tap  water  and  10  c.c.  of 
the  mixture  (containing  0-5  gramme  of  the  mud)  made  up  to 
100  c.c.  with  distilled  water,  when  Tidy's  permanganate  process 
may  be  performed. 

The  dissolved  oxygen  absorption  at  18°  C.  in  twenty-four 
hours  may  be  determined  on  i  or  5  grammes  of  wet  mud  (accord- 
ing as  the  mud  is  foul  or  otherwise)  by  allowing  the  mud  to  remain 
in  an  airtight  bottle  in  contact  with  a  relatively  large  volume  of 
water  containing  oxygen  in  solution;  and  Winkler's  process,  as 
modified  by  Rideal  and  Stewart,  may  be  employed  (pp.  152  and 
153).  A  highly  nitrogenous  mud  will  usually  take  up  much 
oxygen,  and  fine  sulphide  of  iron  undergoes  oxidation  very 
readily.  The  absorption  of  dissolved  oxygen  by  polluted  muds 
goes  on  for  very  long  periods,  but  the  twenty-four  hours'  test 
serves  for  comparative  purposes;  indeed,  as  there  are  no  recog- 
nized standards,  the  presence  and  amount  of  contamination  by 
animal  matter  are  best  proved  by  comparing  the  results 
obtained  with  those  furnished  by  the  mud  collected  at  other 
parts  of  the  river  bed,  which  are  obviously  remote  from  possible 
contamination. 


PART   III 

SOIL   EXAMINATION 

THE  ANALYSIS  OF  SOILS 

The  sanitarian  will  not  often  find  it  necessary  to  make  a  chemical 
analysis  of  soil;  he  may  want  to  classify  soils  and  to  examine 
them  for  f cecal  pollution;  but  generally  for  his  purposes  laboratory 
results  are  of  very  secondary  importance  to  those  of  observations 
made  upon  the  soil  in  situ. 

Although  the  power  of  absorbing  and  retaining  moisture  is  a 
consideration  of  the  first  importance  from  a  health  view- 
exercising  as  it  does  an  important  influence  upon  the  health  of 
whole  communities — yet  it  is  of  litcle  practical  value  to  perform 
any  tests  in  this  connection  upon  small  quantities  of  soil  which 
are  collected  and  brought  to  a  laboratory.  The  amount  of 
moisture  retained  is  so  largely  dependent  upon  local  factors 
that  the  most  reliable  and  valuable  information  is  always  ob- 
tained by  observations  of  the  soil  in  situ.  The  amount  of 
moisture  in  a  sample  of  soil  would  be  ascertained  by  drying  50 
grammes  on  the  water-bath,  and  then  placing  in  the  hot-air  oven 
at  95°  C.  until  the  weight  is  constant. 

The  depth  of  the  ground  water  and  the  extent  of  its  fluctua- 
tions are  often  of  great  importance.  The  digging  of  trial-holes 
will  enable  the  height  of  the  ground  water  to  be  ascertained, 
and  the  fluctuations  in  the  level  of  the  ground  water  may  be 
determined  by  some  arrangement  similar  to  that  shown  in  Fig.  19, 
which  sufficiently  explains  itself. 

The  method  of  testing  the  capacity  which  the  soil  possesses 
for  holding  water  is  obvious:  The  dried  soil  is  weighed  in  a 
cylinder  and  then  saturated  with  water  (this  may  take  hours 
in  the  case  of  clay) ;  the  water  is  allowed  to  drain  off  through  very 

157 


158 


LABORATORY  WORK 


fine  muslin  until  no  more  drops  fall,  and  the  soil  is  then  reweighed; 
the  difference  in  the  two  weighings  represents  the  weight  of  water 
the  known  weight  of  soil  is  capable  of  holding. 

In  collecting  samples  it  must  be  borne  in  mind  that  the  char- 
acters of  the  soil  may  vary  within  small  areas  and  at  different 
depths,  so  that  many  samples  may  have  to  be  collected  and 
analyzed  before  one  can  speak  with  accuracy  of  the  composition 
of  the  soil  of  a  small  area.  These  samples  may  be  taken  by  a 
long,  narrow  spade,  or  by  means  of  an  ordinary  i:^-  to  2  inch  auger 
screwed  into  the  soil ;  and  2  or  3  kilogrammes  must  be  collected 


FIG.    19. ARRANGEMENT   FOR    REGISTERING   THE   VARYING    LEVELS    OF   THE 

GROUND    WATER. 

A,  a  float;  B,  a  pulley;  C,  an  index;  D,  a  graduated  scale.  Opposite  the 
scale  D  a  narrow  glass  window  is  provided  so  that  the  scale  can  be 
seen  without  disturbing  the  arrangement. 

for  analysis.  The  depth  of  the  surface  soil  varies  considerably 
in  different  localities.  In  uncultivated  grounds  it  generally 
occupies  only  a  few  inches  in  depth  on  the  surface,  and  in  culti- 
vated grounds  its  depth  is  generally  the  same  as  that  to  which  the 
implements  used  in  cultivation  have  penetrated;  which  is  gener- 
ally from  9  to  12  inches. 

Soil  is  composed  of  laj'ers  of  more  or  less  disintegrated  rock 
and  quantities  of  organic  matter  resulting  from  the  decay  of 
plants  and  animals.  Entering  into  its  composition  are:  The 
earths — silica,  alumina,  lime  and  magnesia;  the  alkalies — soda. 


THE    ANALYSIS    OF    SOILS  159 

potassa  and  ammonia;  the  acids — sulphuric,  hydrochloric,  car- 
bonic, nitric,  phosphoric,  silicic  and  humic;  oxide  of  iron  and 
small  portions  of  other  metallic  oxides;  a  considerable  propor- 
tion of  moisture  (chiefly  as  a  liquid  film  enveloping  the  particles) ; 
several  gases,  and  micro-organisms.  In  addition  to  the  so-called 
"  nitrifying  organisms,"  there  are  some  which  reduce  nitrates  to 
ammonia,  and  others  that  will  fully  oxidize  ammonia  in  the  pres- 
ence of  air,  but  will  reduce  nitrates  to  ammonia  in  the  temporary 
exclusion  of  air.  The  variable  amount  of  vegetable  and  animal 
matter  gaining  access  is  either  partially  or  wholly  decomposed, 
and  is  ultimately  converted  into  water,  carbonic  acid  and  nitric 
acid  by  the  action  of  micro-organisms.  Of  the  mineral  matters, 
either  silica,  silicates  and  double  silicates,  or  calcium  and  mag- 
nesium carbonates,  generally  predominate.  All  soils  contain, 
though  in  different  proportions,  the  chief  mineral  constituents 
which  are  found  in  the  ash  of  the  plants  which  grow  upon  them ; 
and  an  examination  of  such  ash  will  often  afford  a  rough-and- 
ready  clue  to  the  constitution  of  the  soil.  The  colour  of  soil 
depends  mainly  upon  the  amount  of  humus,  oxide  of  iron  and 
moisture.  A  dried  soil  is  always  much  lighter  in  colour  than 
when  the  moisture  is  present. 

The  less  weathered  stratum,  which  lies  immediately  under  the 
soil,  is  called  the  subsoil,  into  the  composition  of  which  com- 
paratively little  organic  matter  enters.  Sometimes  this  subsoil 
is  porous  sand  or  gravel;  sometimes  light  and  loamy  and  closely 
similar  to  the  superimposed  soil;  sometimes  stiff  (clayey)  and 
more  or  less  impervious  to  water.  The  subsoil  is  generally  lighter 
in  colour  than  the  soil,  and  its  depth  is  usually  limited  by  deposits 
of  undecomposed  or  partly  decomposed  rock  matter,  or  by 
deposits  of  clay,  sand,  or  gravel. 

The  Classification  of  Soils. 

The  sample  having  been  collected,  the  coarser  stones  should 
be  removed,  and  all  lumps  broken  up  so  far  as  possible  with  a 
wooden  pestle. 

The  mechanical  analysis  of  soils,  or  the  sorting  of  the  con- 
stituent particles  into  groups,  is  effected  either  bj^  a  stream  of 
running  water  or  by  allowing  the  turbid  mixture  of  soil  and 
water  to  settle  during  varying  periods  of  time,  after  the  coarser 
particles  have  been  removed  and  sorted  by  sieves  of  different- 
sized  meshes. 


l6o  LABORATORY  WORK 

Schloesing  has  insisted  upon  the  neeessity  of  iiist  treating  the 
soil  with  dilute  acid  and  subsequently  washing  it,  and  of  adding 
ammonia  to  the  water  in  which  it  is  afterwards  to  be  suspended. 
The  acid  dissolves  calcium  carbonate  and  decomposes  "  humates," 
and  the  liberated  humic  acid  is  dissolved  by  the  ammonia.  Other- 
wise the  humates  (if  abundant)  and  the  chalk  tend  to  bind 
together  the  finest  particles,  which  flocculate  into  loose  aggregates 
which  ma^'  not  get  disintegrated.  The  acid  emploj^ed  is  too 
weak  to  dissolve  any  appreciable  amount  of  mineral  constituents 
other  than  calcium  carbonate. 

The  groups  of  particles  obtained  in  a  mechanical  analj^sis  do 
not  possess  any  definite  chemical  individuality.  The  coarser 
fractions  may  contain  fine  grains  of  quartz,  particles  of  clay, 
ferric  oxide,  etc.  It  is  likely  that  the  phj^sical  properties  of  the 
soil  depend  rather  on  the  size  than  on  the  chemical  composition 
of  the  constituent  particles. 

Special  apparatus  has  been  devised,  both  for  thoroughly 
crushing  and  also  for  washing  and  separating  the  various  soil 
constituents  seriatim.  Knopp's  set  of  sieves  is  useful  for  the 
purpose  of  classifying  the  coarse  constituents  of  some  soils. 
The  soil  is  first  dried,  and  then  the  lumps  of  soil  are  crushed  up 
with  the  fingers  and  placed  upon  the  top  sieve  with  the  coarsest 
meshes ;  no  hard  pestle  must  be  used  for  the  crushing,  or  miineral 
particles  would  be  disintegrated  or  broken.  After  thorough 
shaking,  the  particles  all  separate  out  on  one  of  six  sieves,  and 
the  very  fine  material  collects  on  a  tray  at  the  bottom  of  the 
apparatus.  This  latter  material  may  be  classified  by  means  of 
elutriation,  or  washing. 

Particles  collecting  on  the  top  sieve  are  more  than  7  milli- 
metres in  diameter,  and  =  coarse  gravel ;  those  collected  on  the 
second,  between  7  and  4  millimetres,  Rnd=  medium  gravel; 
on  the  third  between  4  and  2  millimetres,  and  =  fine  gravel  ; 
on  the  fourth,  between  2  and  i  millimetres,  Sind=  coarse 
sand  ;  on  the  fifth,  between  i  and  0-3  millimetre,  3.nd=  medium 
sand;  on  the  bottom,  finer  than  0-3  millimetre,  smd—fine 
sand. 

What  remains  upon  each  sieve  is  weighed,  and  the  results  are 
expressed  as  percentages  of  the  total  weight. 

Kiihn  classifies  everything  coarser  than  5  millimetres  as  stones  ; 
between  5  and  3  millimetres,  as  coarse  gravel ;  between  3  and 
2  millimetres,  as  fine  gravel ;  between  2  and  i  millimetres,  as 


THE   ANALYSIS   OF   SOILS 


i6i 


pearl  sand  ;  finer  than  0-5  millimetre,   as  fine  sand  ;  and  the 
portion  separable  by  elutriation,  as  eaYth. 

Elutriation  may  be  performed  by  the  washing  cylinder  of 
Knopp.  This  consists  of  a  glass  cyhnder  55  centimetres  high,  to 
which  are  attached  four  glass  tubes  fitted  with  taps  at  intervals 
of  10  centimetres.  The  soil  material  which  passes  through  a 
0-3  millimetre  sieve  is  placed  in  the  cyhnder,  and  this  is  filled 
with  water  to  10  centimetres  above  the  highest  tap.  The  whole 
is  well  shaken  for  five  minutes,  and  then  allowed  to  stand  for 
another  five  minutes,  when  the  top  tap  is  opened  and  the  cloudy 
water  allowed  to  escape  into  a  weighed  dish.  The  material 
drawn  off  from  the  second  and  third  and  fourth  taps  is  similarly 


ilill 


4 


'^ iHii^ 

FIG.    20. KNOPP'S    SOIL-WASHING    CYLINDER. 

collected.  The  separate  cloudy  waters  are  then  evaporated  and 
the  residues  weighed;  and  the  fine  sandy  residue  at  the  bottom 
of  the  cyhnder  is  also  collected  and  weighed.  In  this  manner 
the  clayey  matter  in  the  fine  soil  can  be  further  classified  and 
compared  with  similar  observations  on  other  soils. 

To  constitute  pure  clay  the  particles  should  not  exceed  o-oi 
milfimetre,  and  the  material  should  be  previously  treated  with 
sufficient  hydrochloric  acid  to  dissolve  out  any  carbonates;  the 
washed  son  should  then  be  boiled  for  half  an  hour  with  10  per 
cent,  ammonia  to  dissolve  humus,  and  the  residue,  washed,  dried, 
and  ignited,  may  be  weighed  as  clay.  This  method  is  suffi  ciently 
exact  for  practical  purposes. 

Poquillon  advocates  the  following  method  of  estimating  clay: 


l62  LABORATORY   WORK 

Ten  grammes  of  the  soil  are  rubbed  up  with  25  c.c.  of  water, 
and  the  hquid  mixed  with  100  to  120  c.c.  of  a  o-i  per  cent, 
solution  of  ammonium  chloride  and  left  for  five  minutes.  The 
supernatant  liquid  is  then  decanted;  the  operation  is  repeat-ed 
six  to  eight  times  until  the  washings  are  clear,  when  the  residual 
sand  is  washed,  first  with  dilute  hydrochloric  acid  and  then  with 
water,  dried  and  weighed.  The  turbid  wasliings  are  mixed, 
•acidified  with  hj'drochloric  acid,  left  for  two  or  three  hours, 
when  the  precipitated  clay  is  collected  on  a  filter,  washed  with 
water,  dried,  and  weighed. 
The  amount  of  sand  in  clay  is  usually  estimated  as  follows : 
Heat  a  weighed  quantit}'  of  the  dried  fine  material  with  sul- 
phuric acid;  then  boil  with  water,  collect  the  insoluble  matter 
on  a  tared  filter,  dr}^  and  weigh;  remove  and  boil  an  aliquot 
part  of  this  insoluble  matter  with  a  strong  solution  of  sodium 
carbonate,  and  weigh  the  insoluble  residue  as  sand. 

Lime  may  be  estimated  by  treating  the  earth  in  a  litre  shaking- 
flask  for  half  an  hour  with  500  c.c.  of  standardized  hydrochloric 
acid  (containing  about  -J  per  cent,  oi  hydrogen  chloride),  and 
titrating  an  aliquot  part  with  soda,  using  phenolphthalein  as 
indicator. 

The  simplest  apparatus  for  a  silt  estimation  takes  advantage  of 
the  relative  rates  of  descent  of  the  various  soil  particles  through 
water  at  rest.  The  chief  disadvantage  of  silt  methods  is  the 
tendency  of  the  fine  particles  to  aggregate  and  form  small  lumps 
which  act  as  larger  particles.  The  only  means  of  obtaining 
a  perfect  separation  of  the  soil  particles  are  by  boiling  for  one 
hour  with  water,  and  by  wet  pestling.  Even  then  it  has  been 
demonstrated  that  particles  of  the  different  sizes  are  represented 
throughout  the  entire  deposit.  Doubtless  the  finest  particles 
are  best  separated  by  elutriation. 

An}'  soil  containing  less  than  5  per  cent,  of  chalk,  which  is  not 
so  rich  in  vegetable  matter  as  to  constitute  a  "  peaty  "  one,  and 
which  contains  not  over  10  per  cent,  of  clay  and  excess  of 
sand=  a  "  sandy  soil."  If  such  soil  contains  10  to  40  per  cent. 
of  clay  and  excess  of  sand  =  a  "  sandy  loam."  If  40  to  70  per 
cent,  of  clay=  a  "  loamy  soil."  If  70  to  85  per  cent,  of  clay=  a 
"  clay  loam."  If  85  to  90  per  cent,  of  clay=  a  "  strong  clay  soil." 
Sand  makes  a  soil  friable,  gives  it  a  low  specific  heat  and  the 
power  of  draining  quickly. 

A  clay  soil  containing  no  sand  at  all=  a  "pure  agricultural 


THE   ANALYSIS    OF    SOILS  163 

day''  which  is  essentially  silicate  of  alumina  mixed  with  small 
quantities  of  organic  matter,  lime,  magnesia  and  ferric  oxide. 
The  different  varieties  of  clay  are  mainly  due  to  the  varying 
amounts  of  these  latter  substances. 

Strong  clays  absorb  and  retain  nearly  three  times  as  much 
water  as  sandy  soils,  while  peaty  ones  absorb  a  still  larger  pro- 
portion; and  the  same  remarks  broadly  apply  to  the  relative 
readiness  with  which  water  is  lost  by  evaporation  from  these 
soils. 

If  there  is  more  than  5  per  cent,  of  chalk,  the  remainder  con- 
sisting mainly  of  clay,  the  soil  is  called  a  "  marl  "  ;  and  if  there 
is  more  than  20  per  cent,  of  chalk,  "  calcareous." 

"  Peaty  "  soils  generally  contain  from  60  to  80  per  cent,  by 
weight  of  organic  matter;  "  rich  cultivated  soils,"  from  about 
5  to  20  per  cent. ;  and  "  stiff  clayey  "  ones,  from  2  to  10  per  cent. 

By  means  of  vegetation,  and  owing  to  the  fixation  of  free 
nitrogen  by  soil  micro-organisms  and  plants,  even  a  sandy  soil 
may  in  time  become  productive. 

To  ascertain  the  substances  which  a  water  will  extract  from 
soil  and  hold  in  solution,  Schulze's  method  is  recommended  by 
Fresenius.  The  necks  of  several  middle-sized  funnels  are  closed 
with  small  filters  of  strong  filter-paper;  these  are  moistened, 
and  the  paper  pressed  close  to  the  sides  of  the  funnel;  the  air- 
dried  soil  is  then  introduced  in  small  lumps  ranging  in  size  from 
a  pea  to  a  walnut  (but  not  pulverized,  or  even  crushed)  until  the 
funnels  are  filled  to  about  two-thirds.  Distilled  water  is  now 
poured  on  in  quantity  sufficient  to  cover  the  soil.  If  the  first 
portion  of  the  filtrate  is  turbid,  it  must  be  poured  back  into  the 
funnel,  and  the  filtration  allowed  to  proceed  quietly ;  the  funnels 
are  again  filled  with  water,  and  this  process  of  extraction  is 
continued  until  the  combined  filtrates  weigh  twice  or  three  times 
as  nmch  as  the  soil  used.  The  several  filtrates  are  next  mixed, 
and  the  necessary  analysis  performed  to  obtain  the  desired 
information. 

Alumina  was  never  found  by  Schulze  in  the  aqueous  extract. 

In  most  soils  the  phosphoric  acid  exists  as  a  basic  ferric  phos- 
phate, and  hence  the  great  insolubility  of  soil  phosphates. 

The  smaller  part  into  which  the  non-concentrated  aqueous 
solution  was  divided  is  finally  tested  for  nitric  and  nitrous  acids 
and  ammonia. 


164  LABORATORY   WORK 

As,  however,  the  solvents  which  act  naturally  on  the  soil  are 
something  more  than  distilled  water,  it  is  desirable  to  examine 
those  substances  which  are  soluble  in  carbonic  acid  water,  as  by 
saturating  distilled  water  with  carbonic  acid  and  allowing  this 
to  act  upon  the  soil  for  several  da^-s  in  a  closed  flask,  which 
should  be  well  shaken  from  time  to  time.  Water  containing 
both  carbonic  acid  and  ammonium  chloride  (about  0-05  per  cent.) 
should  also  be  allowed  in  a  similar  manner  to  act  upon  the  soil 
and  the  substances  then  taken  up  should  be  examined. 

Probably  the  best  solvent  for  extracting  from  soil  the  "  avail- 
able "  (as  distinguished  from  "  total  ")  mineral  constituents  for 
lant  food,  is  a  i  per  cent,  solution  of  citric  acid  (Bernard  Dyer). 

The  total  phosphoric  acid  in  soils  should  be  determined  in 
the  manner  recommended  by  Hehner,  as  follows:  The  soil  is 
incinerated  and  digested  with  hj^drochloric  acid,  evaporated  to 
dryness  to  render  silica  insoluble,  redigested  with  acid,  filtered 
and  washed.  The  filtrate  and  washings  are  concentrated  to  a 
small  bulk,  and  treated  in  the  cold  with  excess  of  a  solution  of 
ammonium  molybdate  in  nitric  acid.  After  standing  forty 
hours  in  a  warm  place,  the  liquor  is  decanted  through  a  filter, 
the  precipitate  is  washed  several  times  by  decantation  (first 
with  dilute  nitric  acid,  then  with  very  small  amounts  of  distilled 
water),  and  finally  transferred  to  the  filter  and  washed  free  from 
excess  of  acid.  The  ammonium  phospho-molybdate  is  then 
dissolved  in  ammonia,  evaporated  to  dryness  in  a  platinum 
capsule,  and  dried  to  constant  weight  at  100°  C.  The  residue 
contains  3I  per  cent,  of  its  weight  of  phosphoric  acid.  Or  the 
ammonium  phospho-molybdate  may  be  dissolved  in  ammonia, 
magnesium  mixture  added,  and  the  precipitate  collected,  ignited 
and  weighed  as  MgaPgO^,  which  xo-64=P2^5- 

To  estimate  nitric  acid,  first  rapidly  dry  the  sample  at  about 
60°  C,  so  as  to  stop  nitrification  ensuing  after  the  collection  of 
the  sample ;  extract  1,000  grammes  of  fine  soil  with  2,000  grammes 
of  distilled  water  for  forty-eight  hours,  with  frequent  shaking; 
and  then  filter  1,000  c.c.  of  the  extract  (corresponding  to  500 
grammes  of  the  dry  soil).  A  small  quantity  of  pure  sodium 
carbonate  should  be  added  to  the  filtrate,  which  is  next  evapor- 
ated to  about  100  c.c.  Any  precipitate  which  forms  during 
evaporation  should  be  filtered  off,  when  the  nitric  acid  may  be 
estimated  in  the  filtrate. 

Sulphur  exists  in  soil  as  sulphates  (generally  calcium  sulphate). 


THE    ANALYSIS    OF    SOILS  165 

in  organic  compounds,  and  as  sulpliides  (iron  pyrites).  To 
estimate  the  sulphates  in  soil,  heat  along  with  dilute  hydro- 
chloric acid  for  a  short  time,  then  filter,  and  precipitate  from 
the  filtrate  with  barium  chloride  solution. 

An  examination  for  the  peaty  acids  may  be  made  thus:  Some 
of  the  washed  soil  is  dried  and  sifted,  to  separate  any  straw, 
roots  and  stones;  what  passes  through  a  fine  sieve  is  digested 
for  several  hours  at  about  30°  C,  with  a  solution  of  carbonate 
of  soda,  and  filtered.  The  filtrate  is  then  slightly  acidified  with 
hydrochloric  acid;  and  if  brown  flakes  separate,  these  consist 
of  the  peaty  acids — i.e.,  ulmi'c,  humic,  or  geic.  The  more  ulmic 
acid  is  present  the  lighter  is  the  shade  of  brown;  a  dark  shade 
indicates  a  preponderance  of  humic  or  geic  acids. 

These  flakes  may  be  collected  upon  a  weighed  filter,  washed 
until  the  water  begins  to  be  coloured,  dried  and  weighed.  Then 
burn  the  dry  mass,  deduct  the  weight  of  the  ash  (after  sub- 
tracting the  filter  ash)  from  that  of  the  dry  mass,  and  enter  the 
difference  as  "  acids  of  humus." 

The  total  nitrogen  of  soil  would  be  best  determined  by  Kjel- 
dahl's  process: 

Five  to  ten  grammes  of  the  fine  air-dried  soil  are  placed  into 
a  small  hard  Jena  glass  flask,  and  30  c.c.  of  pure  sulphuric  acid 
are  poured  over  the  soil,  so  as  to  thoroughly  wet  it.  When  all 
the  frothing  has  subsided,  15  grammes  of  potassic  sulphate  are 
added  (to  raise  the  boiling-point),  and  about  ^  gramme  of  colour- 
less (anhydrous)  cupric  sulphate  (as  an  oxidizer),  and  the  mix- 
ture is  heated  until  the  liquid  is  a  yellow  colour.  Then  50  per 
cent,  caustic  potash  solution  (recently  boiled  to  expel  any 
ammonia)  are  added  until  the  liquid  becomes  alkaline,  as  in- 
dicated by  the  circumstance  that  the  copper  is  precipitated  as 
blue  cupric  hydroxide.  The  remainder  of  the  process  is  carried 
out  in  the  manner  described  on  p.  146. 

Example. — 10-55  grammes  of  soil  were  taken. 

The  distillate  received  into  50  c.c.  ^^  sulphuric  acid  required 
27  c.c.  ~  sodic  hydrate  to  neutralize  it. 

.-.  23  c.c.  of  the  /o  acid  have  been  neutralized  by  the  ammonia 
in  the  distillate. 

But  I  c.c.  of  the  y'^  acid=  0-0017  gramme  NH3  or  0-0014 
gramme  of  N. 

.-.  there  are  23  x  0-0014=  0-0322  gramme  N  in  10-55  grammes 
of  soil=  0-3  per  cent. 


l66  LABORATORY   WORK 

The  collection  of  ground  air  and  the  estimation  of  carbonic 
acid  are  dealt  with  in  Air  Analysis. 

It  is  occasionally  desirable  to  know  whether  the  soil  has  been 
recently  polluted  with  excremental  matter.  The  filtered  aqueous 
extract  (obtained  b}^  acting  upon  a  known  weight  of  dried  soil 
with  distilled  water  for  forty-eight  hours,  with  frequent  stirring) 
can  in  these  cases  be  examined  for  oxidized  nitrogen,  chlorine, 
and  organic  matter,  and  the  amounts  thus  obtained  compared 
with  those  procured  from  similar  soil  in  the  neighbour- 
hood. 

In  100  parts  of  soil  dried  in  the  air  Krocker  found  that  clayey 
soils,  before  manuring,  yielded  o-i  to  0-45  of  ammonia;  loamy 
soils,  0-13;  sandy  soils  (ne\er  cultivated),  about  0-05;  and 
marls,  0-004  to  o-og  of  ammonia. 

Ferrous  sulphide  is  always  in  evidence  in  foul  sewage  deposits 
and  in  mud  exposed  to  gross  sewage  contamination.  Its  presence 
has  been  explained  by  fermenting  organic  matter  reducing  ferric 
oxide  or  hydrate  to  ferrous  compounds;  then  some  of  the  sul- 
phuretted hydrogen  from  the  decomposition  of  organic  matter 
forms  the  ferrous  sulphide;  and  carbonic  acid,  acting  on  ferrous 
sulphide,  is  capable  of  producing  the  sulphuretted  hj^drogen 
which  may  cause  an  offensive  nuisance  (vide  pp.  122  and  155). 

As  would  be  inferred,  the  soil  of  graveyards  above  the  burial 
level  does  not  materially  differ,  as  regards  the  amount  of  organic 
matter  and  its  products,  from  similar  soil  (unmanured)  elsewhere; 
but  that  taken  on  the  level  of  the  cofhns  and  from  a  short  dis- 
tance below,  is  relatively  richer  in  organic  matter.  Such  soil  is 
found  to  be  somewhat  richer  in  bacteria  than  other  unmanured 
soils,  and  more  especially  is  this  the  case  with  that  lying  around 
the  top  of  the  coffins  (Reiners,  Fraenkel,  Young). 

The  various  manures  with  which  the  soils  under  cultivation 
are  dressed  necessarity  effect  considerable  changes  in  the  con- 
stitution of  the  original  soil,  besides  yielding  abundance  of 
soluble  matter  to  the  water  which  comes  in  contact  with  them. 
The  commoner  manures  are — 

Farm^'ard  and  animal  excrement  and  "guano";  bone  dust 
and  other  phosphatic  manures  (calcium  phosphate),  etc. ;  vege- 
table manures — sawdust,  soot,  charcoal,  peat,  and  seaweed; 
ammonia  salts,  especially  the  sulphate;  sodium  salts,  especially 
the  nitrate;  potassium  salts,  especially  the  chloride,  nitrate,  and 
phosphate;  and  gypsum. 


THE    ANALYSIS    OF    SOILS  167 

The  following  are  some  of  the  recommendations  of  a  Com- 
mittee of  the  Agricultural  Education  Association : 

Taking  Samples. — Under  ordinary  conditions  the  sample  shall 
be  taken  to  a  depth  of  9  inches,  but  in  case  of  shallow  soils  to 
such  lesser  depths  as  mark  a  natural  line  of  demarcation. 

The  committee  approves  of  the  use  of  the  auger  as  one  method 
that  may  be  adopted  for  taking  samples.  Several  cores  should 
be  taken  and  mixed  for  analysis. 

Drying. — The  sample  shall  be  air-dried  for  analysis.  The 
drying  may  be  accelerated  by  heating  to  a  temperature  not  ex- 
ceeding 40°  C,  but  in  all  cases  the  soil  should  be  finally  left,  for 
a  day  or  two,  spread  in  a  thin  layer  and  exposed  to  the  air  at 
the  ordinary  temperature  of  the  room. 

Sifting. — A  sieve  with  round  holes  3  millimetres  in  diameter 
shall  be  used  to  separate  the  fine  earth  for  analysis  from  the 
stones  and  gravel.  Gentle  pressure  with  a  wooden  or  caoutchouc 
pestle,  or  other  means,  may  be  adopted  to  break  up  aggregates  of 
clay  and  silt,  but  care  should  be  taken  not  to  crush  any  of  the 
stones  or  lumps  of  chalk. 

For  determination  of  the  "  available  constituents  "  the  "  fine 
earth  "  is  used  without  grinding.  For  the  other  determinations 
100  grammes  or  more  of  "  fine  earth  "  is  sifted  through  a  woven 
sieve  of  40  meshes  to  the  inch,  or  a  sieve  with  round  holes  of 
I  millimetre  in  diameter.  What  is  retained  by  the  sieve  is  ground 
till  it  will  pass  through,  and  the  whole  mixed. 

Determination  of  Carbonate  of  Lime. — The  carbon  dioxide 
evolved  on  treatment  of  the  fine  earth  with  acid  is  calculated 
as  carbonate  of  lime. 

This  is  regarded  as  a  convenient  measure  of  the  "  available 
basicity  "  of  the  soil,  without  discriminating  between  carbonates 
of  lime  and  magnesia. 

Determination  of  Total  Mineral  Constituents. — The  fine  earth 
is  boiled  with  strong  hydrochloric  acid  in  an  open  flask  for  a 
short  time  in  order  that  the  acid  may  attain  constant  strength, 
and  then  digested  at  the  ordinary  water-bath  or  steam-oven 
temperature  for  forty  to  forty-eight  hours,  the  flask  being  loosely 
stoppered.  In  this  solution  the  phosphoric  acid  and  potash  are 
determined,  and  other  mineral  constituents  as  desired. 

The  object  is  to  obtain  as  thorough  an  extraction  of  the  soil 
as  is  possible,  short  of  ultimate  analysis.  The  period  for  the 
extraction  is  made  sufficiently  long  to  minimize  errors  due  to 


l68  LABORATORY   WORK 

variations  in  the  actual  time,  the  strength  of  the  acid,  or  the 
temperature. 

Unignited  soil  is  taken,  since  ignition  effects  a  drastic  and 
variable  alteration  of  the  constitution  of  the  soil — e.g.,  no  con- 
stant proportion  is  found  between  the  potash  extracted  from 
ignited  and  unignited  soil.  H3'drochloric  acid  is  taken  as  the 
most  generally  effective  solvent;  even  peaty  soils  are  found  to 
yield  as  much  phosphoric  acid  to  hydrochloric  acid  as  to  nitric 
acid  or  aqua  regia. 

The  Bacteriological  Examination  of  Soil. 

From  the  point  of  view  of  an  examination  to  obtain  results 
immediately  available  for  public  health  purposes,  the  bacterio- 
logical examination  of  soil  has  only  a  limited  usefulness. 

Its  utility  from  this  aspect  is  chiefly  in  connection  with  the  con- 
tamination of  water  from  surface  washings. 

The  examination  of  soil  for  B.  typhosus,  B.  pestis,  and  other 
pathogenic  organisms  is,  apart  from  the  pathogenic  anaerobes,  a 
matter  of  great  difficulty.  The  examination  is  made  on  the 
general  lines  laid  down  for  the  isolation  of  these  organisms. 
Thus,  to  detect  the  typhoid  bacillus  in  soil,  the  soil  is  mixed 
thoroughly  with  sterile  water,  and  the  water  examined  for  this 
organism  by  methods  similar  to  those  used  for  its  isolation  from 
contaminated  water. 

A  number  of  investigations  have  been  carried  out  upon  the 
vitality  of  typhoid  bacilli  in  soil.  The  results  show  considerable 
discrepancies.  They  indicate  that  under  experimental  con- 
ditions the  typhoid  bacillus  will  survive  for  many  weeks  (ten 
to  twelve)  in  soil,  but  that  under  natural  conditions  probably 
not  more  than  one  week;  and  that  the  factors  influencing  its 
vitality  are  many  and  varied,  the  antagonism  of  other  microbes, 
and  the  physical  conditions  of  moisture  and  temperature  being 
the  most  important. 

Soils  which  have  been  comparatively  recently  contaminated 
with  organic  matter  in  quantity — for  example,  by  sewage  or 
manure — show  evidence  of  this  when  bacteriologically  examined 
in  the  total  number  of  aerobic  organisms,  the  number  of  spores 
present,  the  number  of  B.  coli,  B.  enteritidis  sporogenes,  and 
streptococci. 

The  following  statement  is  by  W.  G.  Savage: 


THE    ANALYSIS    OF    SOILS  169 

"  In  collecting  soil  for  bacteriological  examination  the  depth 
from  which  it  is  obtained  is  of  fundamental  importance.  If  the 
surface  soil  is  to  be  examined,  scrape  up  with  a  sterile  spatula, 
and  transfer  to  a  sterile  receptacle.  To  obtain  soil  from  a  given 
depth  either  a  fresh  cutting  must  be  made  and  the  soil  collected 
at  the  required  depth,  or,  preferably,  some  form  of  borer  may 
be  used.  For  this  purpose  Fraenkel's  borer  is  convenient,  its 
chief  drawback  being  that  it  holds  only  a  small  quantity  of  soil. 
"  If  Fraenkel's  borer  is  used,  it  is  advisable  to  collect  at  least 
eight  samples  from  spots  about  a  foot  apart,  and  to  mix  together 
to  obtain  a  representative  sample.  Also  in  this  way  sufficient 
soil  will  be  obtained  for  a  concurrent  chemical  examination. 
By  means  of  this  borer  the  exact  depth  of  the  soil  taken  can  be 
ascertained.  Owing  to  its  length  it  cannot  be  sterilized  in  the 
hot-air  oven,  but  it  can  be  conveniently  and  sufficiently  sterilized 
by  pouring  in  methylated  spirit  and  igniting.  After  steriliza- 
tion wrap  the  lower  portion  in  a  sterile  cloth  and  secure  with 
string.  This  plan  is  very  convenient  when  a  number  of  samples 
have  to  be  taken  in  one  day,  and  at,  perhaps,  a  long  distance 
from  the  laboratory,  since  the  borer  can  be  resterilized  at  once 
before  each  sample  is  taken,  it  being  only  necessary  to  carry  a 
bottle  of  spirit  and  a  number  of  sterile  cloths  in  a  metal  box. 
The  soil  is  removed  by  a  sterile  spatula  from  the  interior  of  the 
borer  to  the  steriHzed  tin  or  other  receptacle  used  for  the  soil. 

"  The  examination  should.be  commenced  as  soon  after  collec- 
tion as  possible. 

"  To  estimate  the  total  number  of  bacteria,  and  for  some  other 
steps  of  the  examination,  very  extensive  dilution  must  be  prac- 
tised. As  an  example  of  a  convenient  method  of  dilution  the 
following  procedure  is  given:  other  methods  of  dilution  will 
readily  suggest  themselves.  It  is  important  to  remember  that 
owing  to  a  number  of  inherent  difiiculties  (such  as  the  difference 
of  coherence  of  different  soils)  numerical  estimations  are  only 
relatively  accurate,  and  in  any  case  the  same  method  should  be 
used  throughout  for  each  investigation: 

"  Accurately  weigh  a  small  sterile  glass-stoppered  bottle  con- 
taining 100  c.c.  sterile  water.  Quickly  introduce,  with  a  sterile 
spatula,  I  gramme  of  the  soil  (previously  well  mixed  together) 
into  the  bottle.  With  a  little  practice  i  gramme  can  be  quickl}- 
and  sufficiently  accurately  added.  Mix  very  thoroughly  by  re- 
peated shaking,  if  necessary  breaking  up  the  soil  by  a  pointed 


170 


LABORATORY   WORK 


sterile  glass  rod.  Call  this  solution  '  Dilution  A.'  Allow  the  soil 
particles  to  settle,  then  add  i  c.c.  or  more,  according  to  the  sus- 
pected contamination  of  the  soil,  to  a  sterile  flask  contain- 
ing 100  c.c.  (or,  more  accurately,  99  c.c.)  sterile  water.  Mix 
thoroughly  and  label  '  Dilution  B.'  Van»dng  quantities  of 
Dilutions  A  and  B  are  used  for  the  examination. 

' '  To  obtain  the  total  number  of  aerobic  organisms  make  gelatine 
plates  from  these  dilutions.  Thus,  0-2,  0-5,  i-o  c.c.  Dilution  B  are 
convenient  amounts  to  add  to  the  gelatine  tubes.  For  the  number 
of  organisms  developing  at  37°  C.  use  in  the  same  way  agar  plates. 

"For  the  number  of  spores,  present  as  such,  add  varjdng  amounts 


FIG.    21. FRAENKEL'S    borer. 

Lower  end  shown  with  open  and  closed  soil-chamber. 

of  the  dilutions  to  gelatine  tubes.  Heat  to  80°  C.  for  ten  minutes, 
then  plate,  incubate,  and  count  in  the  ordinary  way. 

"For  B.  coli  various  fractions  of  the  dilutions  are  added  to  tubes 
of  lactose  bile  salt  media.  These  are  incubated  at  37°  C,  and 
those  which  produce  acid  and  gas  are  used  to  inoculate  solid 
media,  and  the  organism  isolated  exactly  in  the  same  way  as  for 
the  isolation  of  this  bacillus  from  water. 

"  Streptococci  and  spores  of  B.  enteritidis  sporogenes  are  exam- 
ined for  by  methods  identical  with  those  used  for  water." 

According  to  Houston  and  Savage,  B.  coli  is  absent,  or  present 
in  small  numbers  only,  in  uncontaminated  soils,  and  is  not 
readily   isolated   even   from   soils   polluted  with   objectionable 


THE    ANALYSIS    OF    SOILS 


171 


animal  matter,  unless  the  contamination  is  gross  in  amount  and 
of  recent  sort.  Houston  found  that  when  sewage  containing 
large  numbers  of  B.  coli  is  added  to  soil  tlie  coli  organisms 
relatively  rapidly  disappear, 

Houston  regards  the  presence  of  the  spores  of  B.  enteriiidis 
sporogenes  as  an  indication  of  contamination,  but  not  necessarily 
recent,  and  the  presence  of  streptococci  as  indicating  very  recent 
contamination.  Experimenting  with  soil  to  which  sewage  (con- 
taining numerous  streptococci)  had  been  added,  he  found  that 
the  addition  of  sewage  to  a  soil  might  be  detected  by  the  presence 
of  streptococci  even  in  a  minimum  amount  of  the  soil  thus 
polhited,  but  that  their  disappearance  seems  to  be  extremely  rapid. 

The  results,  obtained  by  the  writer,  of  a  mineral  analysis  of 
a  few  common  soils  are  given  below.  It  must  be  understood 
that  soils  which  are  called  by  the  same  name  may  vary  con- 
siderably in  the  nature  and  amounts  of  their  less  characteristic 
constituents.  The  main  purpose  of  the  following  analyses  is 
to  afford  an  approximate  idea  of  the  amounts  of  the  more  charac- 
teristic substances  which  enter  into  the  composition  of  a  few  of 
the  more  common  soils: 


Clay  [Stourbridge) 
Silica    .  . 
Alumina 
Organic  matter 
Iron  (oxide)     . . 
Lime     . . 

(carbonate,  1-4) 

(sulphate,     o-i) 
Magnesia,  etc. 
Phosphoric  acid 
Water  . . 


68 
15 

4 

3 

1-5 


traces  0-5 


lOO-O 

Calcareous  [Sussex). 

Lime     . . 

.     90 

(carbonate,  89-5) 

(sulphate,       0-35) 

(phosphate,    0-15) 

Organic  matter 

3 

Oxide  of  iron  and  alumina  . .          .  . 

2-5 

Silica 

0*55 

Magnesia  (carbonate) 

•       0-5 

Water 

•       3-45 

100-00 


172 


LABORATORY   WORK 


Peaty  {Devonshire). 

Organic  matter 
Silica    .  . 
Alumina 
Lime     .  . 
Oxide  of  iron  .  . 
Sulphuric  acid 
Magnesia 
Soda  and  potash 
Phosphoric  acid 


(Air-Dried  Soil.) 


90-5 
7-5 
074 

0-5 
0-46 

0-2 

0-05 
0-03 

0-02 


100-00 

Garden  (Vegetable)  Mould. 

Silica    . . 

•     49-25 

Organic  matter 

•     13-5 

Oxide  of  iron  .  . 

•       9-25 

Carbonic  acid.  . 

7-12 

Lime     .  . 

•       5-13 

Alumina 

•       274 

Soda  and  potash 

•       2-5 

Chlorine 

•       1-5 

Sulphuric  acid 

•       1-3 

Phosphoric  acid 

.       0-4 

Oxide  of  manganese  . 

0-25 

Magnesia 

o-i6 

Water 

.       6-9 

100-00 


PART      IV 

AIR  ANALYSIS 


CHAPTER  I 

THE  NORMAL  CONSTITUENTS  OF  AIR- 
EUDIOMETRY 


-oxygen- 


Composition  OF  THE  Atmosphere  (freed  from  aqueous  vapour) 


In  loo  Volumes. 
78-07 

20-95 

0-95 
0-03 


V  traces. 


Nitrogen 

Oxygen 

Argon    . . 

Carbonic  acid 

Hydrogen 

Ammonia 

Nitric  acid 

Helium,  krypton,  neon,  xenon 

The  amount  of  aqueous  vapour  is  variable,  the  average  in  this 
country  being  1-4  per  cent. 

Suspended  matter  is  also  present  in  variable  nature  and 
amount. 

In  the  air  of  towns  the  carbonic  acid  may  vary  from  0-03  per 
cent,  to  o-o8  per  cent,  and  over  during  the  prevalence  of  a  fog. 
Oxidized  sulphur  and  sulphuretted  hydrogen  are  frequently 
present  in  traces,  as  are  also  ammonia,  marsh  gas,  and  organic 
matter.  During  dense  fog  in  large  town  districts  the  amount  of 
sulphurous  and  sulphuric  acid  present  is  very  much  increased. 

The  air  of  large  towns  is  generally  slightly  acid,  owing  to  the 
sulphurous  and  sulphuric  acids  which  are  derived  from  the 
sulphur  compounds  contained  in  the  articles  used  for  com- 
bustion ;  and  the  air  of  occupied  rooms  in  which  coal  gas  is  burning 

173 


174  LABORATORY   WORK 

may  be  slightly  acid.  A  piece  of  delicate  blue  litmus-paper, 
moistened  \vith  neutral  distilled  water,  commonly  denotes  this 
acidit}'  by  changing  in  an  hour  or  less  to  a  faint,  though  dis- 
tinct, red. 

Oxygen. 

We  haye  seen  that  the  amount  of  oxygen  in  the  external 
atmosphere  may  be  taken  to  constitute  a  normal  percentage  of 
about  20*95.  After  a  careful  consideration  of  the  number  of 
inyestigations  which  have  been  made,  it  seems  that  it  may  reach 
a  slightly  higher  limit  oyer  large  expanses  of  open  countr3%  and 
that,  eyen  in  the  atmosphere  of  occupied  rooms,  it  rarely  falls 
below  2075  per  cent. 

In  some  mines  the  oxygen  has  been  estimated  considerably 
below  20  per  cent.  (Angus  Smith  found  i8-2y  per  cent.,  and 
some  Continental  observers  have  estimated  it  even  lower.) 

The  Estimation  of  the  Amount  of  Oxygen  in 
THE  Atmosphere. 

Eudiometry. 
Apparatus  required.  —  An  eudiometer  {evSloti,  good,  and 
fiirpov,  measure)  is  the  instrument  emplo^^ed  for  measuring 
the  volume  of  a  gas  or  gaseous  mixture.  One  of  the  most  simple 
and  convenient  forms  is  Hempel's  gas  burette.  From  the  accom- 
panying figure  it  will  be  seen  to  consist  of  two  glass  tubes  sup- 
ported on  fiat  stands  and  connected  together  at  their  lowest 
points  by  wide  india-rubber  tubing;  the  tube  which  is  seen  in 
Fig.  22  to  be  held  up  (and  which  will  be  subsequently  referred 
to  as  tube  A)  is  plain,  and  is  continued  full  bore  to  the  top, 
where  it  generally  ends  in  a  slightly  trumpet-shaped  mouth ;  the 
other  tube  (which  will  be  referred  to  as  tube  B)  is  graduated  into 
c.c,  and  narrowed  above  so  as  to  fit  inside  of  a  short  piece  of 
small  india-rubber  tubing,  which  serves  to  connect  it  with  an 
"  absorption  pipette  "  containing  the  absorbing  solution.  This 
apparatus,  as  shown  mounted  upon  a  wooden  stand,  consists 
of  two  glass  bulbs  blown  in  a  fine  glass  tube,  bent  in  the  manner 
portrayed  in  the  figure;  the  lower  globe  has  a  larger  diameter 
than  the  upper,  and  is  capable  of  holding  about  150  c.c.  of  the 
reagent  employed,  while  the  upper  one  should  be  of  at  least 
100  c.c.  capacity. 


EUDIOMETRY 


175 


To  charge  the  absorption  pipette  tlie  hquid  reagent  is  poured 
into  the  upper  bulb,  and  the  air  is  then  sucked  out  of  the  lower 
bulb  through  the  capillary  tube  rising  from  it,  until  the  lower 
bulb  is  filled  and  the  reagent  reaches  into  the  syphon  bend  of  the 
capillary  tube,  but  leaves  the  upper  bulb  almost  empty. 

The  single  "  absorption  pipette  "  is  shown  in  Fig.  22;  but  for 
the  absorption  of  oxygen  it  is  necessary  to  use  "  a  double  pipette." 
Reagents  that  are  affected  by  oxygen  (such  as  pyrogallic  acid 
and  cuprous  chloride)  should  not  be  employed  in  a  single  pipette 


FIG.    22. HEMPEL's    GAS    BURETTE    AND    ABSORPTION    APPARATUS. 

because  the  reagent  in  the  lower  bulb  is  exposed  to  the  general 
atmosphere.  Hempel's  double  pipette  permits  of  the  use  of 
such  reagents  without  this  exposure.  The  double  pipette  is 
shown  in  Fig.  23.  The  first  bulb  is  the  largest  (150  c.c),  and  is 
filled  with  the  absorbent;  the  next  is  empty;  the  third  contains 
water;  and  the  fourth  is  empty.  Thus,  when  any  gases  are 
passed  over  into  the  "  pipette,"  the  water  in  the  third  bulb 
passes  into  the  fourth  to  make  room  for  the  gas,  and  thus  shuts 
out  the  atmosphere,  the  absorbing  reagent  only  coming  in 
contact  with  the  small  amount  of  air  originally  in  the  second 
bulb. 


176  LABORATORY   WORK 

Reagents  Employed. — A  solution  of  pyrogallic  acid  and  caustic 
potash — i.e.,  15  grammes  of  the  acid  and  50  of  caustic  potash, 
to  the  htre  of  distilled  water. 


The  Process. 

1.  A  certain  amount  of  atmospheric  air  is  first  measured  in 
the  gas  burette  in  the  following  manner:  Both  tubes  are  placed 
upon  a  level  surface,  and  distilled  water,  which  has  been 
thoroughly  shaken  up  in  the  air  and  thus  mechanically  saturated 
with  it,  is  poured  down  the  plain  tube  A  until  each  tube  is  about 
half-full.  Now  if  the  tube  A  is  raised  the  height  of  the  water 
in  B  will  ascend  until  it  fills  the  tube  B;  and  when  the  tube  A  is 
subsequently  lowered  the  atmospheric  air  of  the  compartment 
will  pass  into  the  graduated  tube  B,  where  it  can  be  imprisoned  by 
turning  the  greased  cock  at  its  mouth.  The  volume  of  air  thus 
collected  is  next  exposed  to  the  same  atmospheric  pressure  as 
obtains  in  the  room  by  adjusting  both  tubes  so  that  the  water 
stands  at  the  same  level  in  each.  An  accurate  reading  is  then 
taken  of  the  volume  of  air  collected.  It  is  convenient  to  take 
about  100  c.c. 

2.  Connection  is  then  made,  as  shown  in  the  figure,  by  fine, 
stiff  india-rubber  tubing,  between  the  burette  and  the  "  absorp- 
tion pipette  " ;  the  latter  being  raised  close  to  the  top  of  the  tube 
containing  the  air,  since  it  is  desirable  to  have  as  short  a  length 
of  tubing  as  possible. 

3.  A  background  of  white  enamel  serves  to  make  the  coloured 
absorbing  liquid  which  rises  in  the  capillary  tube  distinctly 
visible,  and  enables  the  precise  height  to  which  it  reaches  to  be 
carefully  marked. 

4.  Next,  by  liberating  the  clasp  upon  the  tubing  and  opening 
the  greased  cock  above  referred  to,  the  gas  burette  and  absorp- 
tion pipette  are  put  into  communication  with  each  other;  when 
by  raising  the  tube  A  the  air  is  forced  over  into  the  absorption 
pipette.  The  cock  on  the  burette  is  then  closed,  the  india-rubber 
tubing  is  pinched,  and  a  firm  clasp  applied,  after  which  the 
pipette  may  be  disconnected  and  gently  shaken. 

5.  When  absorption  has  taken  place,  by  reconnecting  the 
absorption  apparatus  with  the  burette,  opening  the  cock  and 
removing  the  clasp,  the  residual  air  can  be  brought  back  into 
the  burette  by  lowering  the  tube  A;  care  being  taken  that  the 


EUDIOMETRY  I77 

absorbing  solution  does  not  pass  beyond  where  it  originally  stood 
in  the  connecting  capillary  tube,  as  indicated  by  the  mark  on 
the  porcelain. 

6.  The  air  may  be  thus  treated  several  times,  in  order  to  give 
the  solution  time  to  absorb  all  the  oxygen. 

7.  Before  making  the  final  reading  the  height  of  the  water  in 
the  two  tubes  is  brought  to  the  same  level,  just  as  it  was  at  the 
commencement  of  the  process  (and  for  the  same  reason),  and  then 
the  volume  which  the  air  now  occupies  is  read  off.  A  constant 
reading  should  be  obtained. 

8.  The  volume  remaining  is  broadly  due  to  nitrogen,  and  the 
difference  between  it  and  the  original  volume  represents  the  oxygen 


FIG.   23. — HEMPEL'S    double    ABSORPTION    PIPETTE. 

and  CO2  absorbed.  The  solution  of  pyrogallic  and  caustic 
potash  will  also  absorb  sulphuretted  hydrogen,  sulphurous  acid, 
and  hydrochloric  acid  (if  present).  From  the  percentage  loss  in 
the  volume  of  the  air  by  this  treatment  the  percentage  amount 
of  CO2  (estimated  by  Pettenkofer's  process,  and  calculated  to  the 
same  temperature  and  pressure)  must  be  deducted,  and  the 
remainder  will  represent  the  percentage  amount  of  oxygen  at  the 
current  temperature  and  pressure. 

Example. — The  volume  of  air  collected  in  the  burette  at  the 
current  temperature  and  pressure  was  50*6  c.c.  The  volume  of 
the  residual  air  after  treatment  was  40*0  c.c.  Therefore  the  loss 
is  I0'6  c.c.  in  50'6  c.c.  =  approximately  20-95  per  cent.  Assuming 
that  the  COg  in  the  air  of  the  room  has  been  found  to  be  0"05  per 

12 


T78  LABORATORY   WORK 

cent.,  the  ox3'gen  would  amount  to  approximately  (20*95  -  0'05)  = 
20-90  per  cent.,  at  the  current  temperature  and  pressure. 

Notes. — At  temperatures  of  about  15°  C.  the  last  trace  of  oxygen 
is  thus  removed  in  about  three  minutes  of  shakmg  (Hempel). 

Since  the  conditions  of  temperature  must  remain  the  same 
throughout  the  estimation,  the  gas  burette,  after  it  has  been 
charged,  should  not  be  handled  except  by  its  iron  or  wooden 
stand,  and  the  apparatus  must  not  be  moved  about  from  one 
spot  to  another. 

The  absorbing  reagent  should  always  first  be  saturated  at 
the  current  temperature  and  pressure  by  shaking  it  up  with 
gases  that  are  but  slightly  soluble  in  it,  otherwise  errors  of 
estimation  result;  the  necessity  of  always  thus  saturating  the 
water  in  the  burette  with  the  gas  under  examination  has  been 
mentioned.  With  this  precaution  this  method  of  eudiometry 
gives  results  but  little  inferior  to  those  obtained  by  working  over 
mercury  and  using  solid  absorbents. 

Mr.  J.  F.  Spencer  has  designed  a  four- way  tap  and  connections, 
fitted  to  the  top  of  the  burette,  which  permits  of  the  absorbing 
liquid  being  brought  right  up  to  this  tap,  so  that  on  turning  the 
tap  the  gas  in  the  burette  can  be  brought  directly  in  contact  with 
the  absorbing  hquid,  without  any  intervening  air  space. 

The  oxygen  may  also  be  estimated  by  Dumas'  process,  in 
which  the  air,  having  been  freed  of  its  carbonic  acid  by  aspirating 
through  a  strong  solution  of  caustic  potash,  is  passed  through  a 
combustion  tube  containing  a  length  of  pure  spongy  metallic  cop- 
per. The  copper  is  kept  ignited,  and  becomes  tarnished  by 
oxidation;  the  difference  in  weight  of  the  original  copper  and  the 
tarnished  metal  represents  the  oxygen  taken  up  from  the  volume 
of  air  experimented  upon. 


CHAPTER  II 

CARBONIC    ACID 

The  estimation  of  the  carbonic  acid  in  the  atmosphere  is  of  great 
value.  This  is  not  because  the  carbonic  acid  is  hable  to  exist  in 
injurious  amounts  even  under  the  worst  conditions  of  ventilation 
commonly  obtaining,  but  because  this  gas,  when  furnished  by 
respiration,  may  afford  an  important  clue  to  the  general  condition 
of  the  atmosphere. 

It  is  therefore  the  knowledge  of  the  amount  of  carbonic  acid 
which  has  been  added  to  the  atmosphere  by  respiration  which  is 
generally  required. 

So  inert  is  carbonic  acid  per  se  that  it  may  exist  to  the  extent 
of  2  to  3  parts  per  lOO  without  serious  consequences,  and  fatal 
results  would  not  accrue  with  less  than  from  5  to  10  per  cent. 

The  amount  of  carbonic  acid  which  is  present  in  a  pure  atmo- 
sphere, and  which  may  be  termed  "  normal,"  is  0-033  per  cent, 
by  volume. 

The  lowest  estimation  of  carbonic  acid  made  in  any  atmosphere 
was  0-02  per  cent.,  in  air  at  a  very  high  altitude. 

The  external  atmosphere  of  cities,  during  fogs,  often  contains 
'0-07  per  cent.,  and  may  contain  as  much  as  o-og  per  cent,  or 
even  more. 

In  ill-ventilated  sitting-rooms,  well  lighted  by  gas,  the  carbonic 
acid  often  reaches  0-2  per  cent. 

Where  there  is  "  overcrowding  "  it  has  been  estimated  as  high 
as  07  per  cent.,  and  it  is  commonly  under  these  circum- 
stances 0-3. 

Angus  Smith  found  in  the  worst  parts  of  theatres  0-32  per 
cent. 

We  are  indebted  to  Pettenkofer  for  a  method  of  estimation 
which,  owing  to  the  facility  of  its  performance  and  the  accuracy 
of  its  results,  is  very  generally  adopted. 

179 


l80  LABORATORY   WORK 

The  Collection  of  Samples  for  the  Estimation  of  Carbonic  Acid 
by  Pettenkofer's  Method. 

For  the  estimation  of  carbonic  acid,  the  samples  of  air  may  be 
conveniently  collected  in  wide-mouthed,  glass-stoppered  bottles 
of  about  4  litres  capacity,  which,  when  used  for  this  purpose,  are 
termed  "  air-jars."  These  must  be  thorouglily  cleansed  in  every 
case  before  use,  and  the  last  washings  should  be  with  ammonia- 
free  distilled  water.  After  the  collection  of  the  sample  the 
stoppers  should  be  tied  dowTi,  and  hermetically  sealed  with  pre- 
pared lard  in  those  cases  where  they  have  to  be  removed.  Lastly, 
a  label  is  attached,  on  which  should  be  written  a  statement  of  the 
current  temperature  and  pressure,  the  date,  the  hour,  the  place 
from  which  the  sample  was  taken,  and  the  nature  and  extent 
of  the  non-human  sources  of  COg  (gas-burners,  candles,  and 
lamps) . 

Following  out  the  principles  ad\'ocated  with  regard  to  water 
samples,  a  sample  of  air  should  be  collected — whether  it  be 
vitiated  by  respiration,  combustion,  trade  processes,  or  by  pro- 
ducts of  decomposition,  etc.- — at  the  time  when,  so  far  as  can 
be  judged,  the  atmosphere  will  afford  its  maximum  evidence 
of  pollution.  In  investigating  the  respiratory  contamination  of 
the  air  of  a  bedroom,  for  instance,  the  sample  should  be  taken 
shortly  before  the  first  riser  quits  the  room — that  is  to  say, 
after  the  room  has  been  occupied  by  its  customary  number  of 
occupants  for  the  greatest  number  of  consecutive  hours. 

The  immediate  proximity  of  gas,  lamp  and  candle  lights, 
stoves  and  fireplaces  should  be  avoided;  and  samples  should 
always  be  taken  at  the  mean  height  at  which  the  air  is  being 
respired. 

For  purposes  of  calculating  the  added  COg  a  comparison  sample 
of  the  external  atmosphere  should  always  be  taken,  since  the  COg 
in  the  external  atmosphere  in  towns  varies  materially  from  time 
to  time. 

The  air  is  made  to  occupy  the  jar  by  either  of  the  following 
methods : 

I.  An  air-jar  may  be  accurately  filled  with  clean  water — which 
can,  with  rare  exceptions,  be  got  upon  the  premises,  and  should 
have  been  previously  boiled — and  then  emptied  and  allowed  to 
drain  in  the  compartment  the  air  of  which  is  to  be  examined. 
A  sample  of  the  air  then  rushes  in  to  fill  the  place  of  the  escaping 


CARBONIC    ACID 


l8l 


water.     At  the  time  of  use  the  water  should  be  at  the  tempera- 
ture of  the  room. 

2.  The  air  may  be  forced  in  by  bellows,  which  are  provided 
with  a  long  nozzle,  which  reaches  well  down  into  the  jar  to  within 
an  inch  of  the  bottom.  This  ensures  that  the  air  which  originally 
occupied  the  jar  will  be  completely  displaced  from  below  up- 
wards. 

3.  The  original  air  in  the  jar  may  be  pumped  out  by  means  of 
a  small  air-pump. 

Angus  Smith  drew  the  air  out  of  the  bottle  by  a  flexible 
bellows-pump,  shown  in  Fig  24. 

For  filling  small  bottles,  J.  S.  Haldane  suggests  a  long  piece 
of  rubber  tubing  reaching  from  the  bottom  of  the  air-jar  to  the 
operator,  who  sucks  in  a  deep  breath  of  air  through  the  tube. 


FIG.  24. 


-THE    FLEXIBLE    BELLOWS-PUMP    EMPLOYED    BY    ANGUS    SMITH 
TO    DRAW    OUT    AIR    FROM    THE    AIR-JAR. 


4.  A  jar  may  be  accurately  filled  with  mercury,  and  emptied 
in  the  compartment  where  the  sample  is  to  be  collected.  Al- 
though this  plan  is  theoretically  the  best,  it  is  practically  in- 
applicable on  account  of  the  large  amount  of  mercury  required, 
and  the  difficulty  of  conveying  this  (from  its  great  weight)  from 
place  to  place. 

The  first  method  is  recommended;  for  it  is  easy  of  execution, 
and  furnishes  satisfactory  results. 

Whenever  it  is  possible,  there  is  a  slight  advantage  in  making 
the  analysis  at  once  in  the  compartment  in  which  the  sample 
has  been  taken,  since  the  general  atmosphere  is  that  of  the 
jar;  and  this  can  sometimes  be  done,  although  it  is  often  very 


l82  LABORATORY   WORK 

incon\'enient.  There  should  be  as  Httle  loss  of  time  as  possible 
in  commencing  the  analysis,  and  in  the  meantime  the  jar  should 
not  be  exposed  to  temperatures  varying  much  from  that  at 
which  the  sample  was  collected. 

The  room  in  which  the  sample  is  analyzed  must  be  free  from 
draughts  and  of  a  uniform  temperature,  or,  at  least,  not  liable  to 
frequent  changes  in  temperature. 

The  error  which  would  be  introduced  by  breathing  into  the 
air-jar  and  reagents,  or  by  handhng  the  jars  more  than  is  abso- 
lutely necessary  with  warm  hands,  is  obvious.  It  is  desirable 
to  hold  the  breath  for  the  few  moments  during  which  the  sample 
of  air  is  being  collected  in  the  air-jar,  the  wide  mouth  of  which 
permits  of  a  rapid  escape  of  its  contained  water. 

Pettenkofer's  Alkalimetric  Method  of  Estimating 
THE  Carbonic  Acid  in  the  Atmosphere. 

The  rationale  of  the  process  is  as  follows:  Clear  baryta  water 
combines  with  carbonic  acid  with  great  readiness,  thereby 
becoming  turbid 

(BA(0H)2  +  CO2  =  BaCOg  +  H2O), 
and  the  carbonic  acid  taken  up  reduces  the  alkalinity  of  the 
bar\'ta  water.  If,  therefore,  the  degree  of  alkalinity  of  a 
measured  quantity  of  bar^'ta  water  is  estimated,  and  then  this 
reagent  is  made  to  take  up  all  the  carbonic  acid  of  a  sample  of 
air,  the  amount  of  carbonic  acid  taken  up  will  be  in  proportion 
to  the  reduction  of  alkalinity  of  the  baryta  water. 

Special  Apparatus : 

I.  An  air-jar  of  about  4  litres  (4,000  c.c.)  capacity.  It  is  necessary  to 
know  the  exact  capacity  of  the  bottle  in  order  that  the  amount  of  air 
which  it  will  hold  may  be  accurately  known.  This  can  be  ascertained  by 
filling  the  bottle  with  as  much  water  as  it  will  hold  when  the  stopper  is 
inserted,  and  then  measuring  the  water  as  it  is  emptied  out;  the  volume 
of  the  water  which  the  bottle  held  will  correspond  to  the  volume  of  air 
which  takes  its  place. 

Chemical  Reagents : 

I.  Pure  clear  baryta  water  (4'5  grammes  of  the  crystallized  hydrate  to 
the  litre)  to  which  about  i  gramme  of  baric  chloride  should  be  added  to 
counteract  the  influence  of  small  quantities  of  alkalies  which  may  be 
present. 

In  order  that  the  barj-ta  water  may  be  kept  quite  pure  it  will  be  necessary 
to  remove  the  carbonic  acid  from  the  air  which  enters  the  store  bottle 
when  some  of  its  contents  are  withdrawn,  by  making  it  pass  through  soda 


CARBONIC   ACID 


183 


lime.  Fig.  25  shows  how  this  can  be  readily  effected :  A  large  glass  store 
bottle  is  represented,  fitted  with  a  syphon  tube  to  draw  off  the  clear  baryta 
water.  Any  air  which  enters  must  pass  through  the  tube  which  is  packed 
with  soda  lime. 

2.  A  standard  solution  of  oxalic  acid  (crystallized)  made  to  such  a 
strength  (i.e.,  2*819  grammes  to  the  litre)  that  i  c.c.  corresponds  to  0-5  c.c. 
of  carbonic  acid  at  the  standard  temperature  and  pressure. 

3.  A  solution  of  phenolphthalein  (i  part  in  250  parts  of  alcohol). 


The  Process. 

1.  A  sample  of  the  air  is  collected  in  the  air- jar. 

2.  Fifty  c.c.  of  perfectly  clear  baryta  water  are  then  placed  in 
the  jar,  and  the  liquid  is  made  to  flow  round  the  sides  of  the  jar 


FIG.    25. STORE    BOTTLE    FOR    BARYTA    WATER. 

by  rolhng  it  about  on  its  side  for  a  minute  or  two  from  time  to 
time.  About  three-quarters  of  an  hour  should  be  allowed  for  all  the 
carbonic  acid  present  in  the  sample  to  combine  with  the  baryta. 
3.  The  alkalinity  of  another  50  c.c.  of  the  clear  baryta  water  is 
meanwhile  tested  in  the  following  manner:  The  50  c.c.  are  placed 
in  a  small  flask  with  a  very  narrow  neck,  and  are  tinted  pink  by 
a  drop  of  phenolphthalein ;  then  the  standard  solution  of  oxahc 
acid  is  cautiously  run  in  from  a  graduated  burette  until  the 
alkalinity  of  the  baryta  water  has  just  been  neutralized  by  the 
acid,  when  the  amount  of  acid  employed  is  read  off  from  the 


184  LABORATORY    WORK 

burette.     The  exact  neutral  stage  is  indicated  by  the  disappear- 
ance of  the  pink  colour. 

4.  At  the  end  of  tliree-quarters  of  an  hour  25  c.c.  of  the 
baryta  water  are  removed  from  the  air-jar,  and  the  causticity 
estimated  as  above.  In  effecting  the  removal  the  precipi- 
tate of  barium  carbonate  which  has  settled  should  not  be 
disturbed. 

5.  The  difference  in  the  number  of  cubic  centimetres  of  acid 
solution  required  to  neutralize  {a)  50  c.c.  of  the  original  baryta 
water,  and  {b)  the  baryta  water  which  has  taken  up  the  carbonic 
acid  of  the  air  in  the  jar,  represents  the  amount  of  carbonic 
acid  in  the  air. 

6.  When  50  c.c.  of  baryta  water  were  added  to  the  jar  an 
equivalent  bulk  of  air  was  displaced.  The  amount  of  air  experi- 
mented upon,  therefore  (assuming  the  capacity  of  the  jar  to  be 
4,000  c.c),  represents  4,000  —  50  c.c.  =  3,950  c.c. 

7.  The  result  must  be  returned  as  the  amount  of  carbonic  acid 
per  cent,  of  the  air  at  the  "  standard  temperature  " — i.e.,  0°  C. — 
and  the  "  standard  pressure  " — i.e.,  760  millimetres  of  mercury— 
since  the  \'alue  of  the  oxalic  acid  solution  is  in  respect  to  CO2  at 
the  standard  temperature  and  pressure. 

Example. — The  causticity  of  50  c.c.  of  the  original  and  clear 
baryta  was  tested  by  cautiousl}^  running  in  the  standard  acid 
solution. 

Twenty  c.c.  of  the  acid  solution  were  required  to  effect  the 
neutralization. 

Twenty-five  c.c.  of  the  baryta  water  from  the  air- jar  required 
only  8-5  c.c.  of  the  acid  solution  to  neutralize  its  diminished 
causticit}^     Therefore,  the  whole  50  c.c.  required  17. 

.•.  20-17  =  3  c.c.  of  the  acid  solution  represents  the  carbonic 
acid  taken  up  by  the  barj^ta  water  from  the  sample  of  air. 

But  I  c.c.  =  0*5  c.c.  of  carbonic  acid. 

.•.  3  c.c.  =  1*5  c.c.  of  carbonic  acid. 

.'.  the  carbonic  acid  originally  in  the  air  sample  amounts  to 
1-5  c.c.  at  the  standard  temperature  and  pressure. 

The  capacity  of  the  jar  was  4,000  c.c,  and  the  air  examined 
is  4,000  c.c.  -50  c.c.  =  3,950  c.c.  at  the  current  temperature  and 
pressure — sa}',  742  millimetres  and  17°  C.  Now,  this  volume  of  air 
has  to  be  converted  to  its  \-olume  at  the  standard  temperature 
and  pressure.  B}'  Bo\'le's  law  the  volume  of  air  varies  inversely 
as  the  pressure.     By  Charles'  law  the  air  contracts  on  cooling 


CARBONIC   ACID  1 85 

^1-^  (  =  0-00366)  of  its  hulk  at  0°  C.  for  every  degree  Centigrade 
down  to  0°. 

The  volume  of  air  experimented  with  wiU  therefore  represent, 
at  the  standard  temperature  and  pressure : 

3950x742 ^        ^930900       ^  3,630  c.c. 


760  X  {i  +  (o'00366  X  17)}     76oxi"o6222 

.-.  there  were  1-5  c.c.  COg  in  3,630  c.c.  of  air,  or  0-0413  per  cent., 
at  the  standard  temperature  and  pressure. 

The  sample  of  the  outside  air  is  similarly  examined,  and  the 
difference  between  the  COg  in  the  inside  and  outside  air  will 
represent  the  added  COg  impurity  of  the  inside  air. 

Notes. — One  c.c.  of  COg  at  0°  C.  weighs  1-96633  milhgrammes 
at  760  millimetres  pressure;  the  relation,  therefore,  between  the 
volume  and  the  weight  =  Y.-y6-V¥¥  =  o '508. 

The  writer  prefers  to  perform  this  process  in  a  long  cylindrical 
jar  of  the  capacity  of  about  3  litres  and  fitted  with  a  doubly  per- 
forated cork,  one  perforation  transmitting  the  drawn-out  point 
of  a  graduated  burette  with  stopcock,  and  the  other  perforation 
a  small  piece  of  glass  tubing  carrying  externally  a  small,  close- 
fitting,  india-rubber  cap.  The  air  is  collected  as  directed; 
50  c.c.  of  baryta  water  (standardized  at  the  time  of  use  by 
decinormal  oxalic  acid)  is  added  through  the  glass  tube,  which 
is  then  sealed  by  its  cap.  After  one  hour,  the  bottle  being  gently 
rolled  along  a  table  from  time  to  time  in  the  meanwhile,  a  few 
drops  of  phenolphthalein  are  added  through  the  small  glass 
tube  (the  cap  of  which  is  now  removed),  the  biirette  is  charged 
with  the  decinormal  oxalic  acid  solution,  and  this  is  allowed  to 
discharge  cautiously  into  the  bottle.  So  soon  as  the  pink  colour 
commences  to  weaken,  the  acid  is  added  slowly  in  drops,  and  the 
bottle  is  gently  shaken  and  stood  upon  a  white  porcelain  slab. 
The  neutral  stage  can  be  readily  noted  when  the  experimenter 
looks  down  from  above  on  to  the  white  porcelain  slab.  This 
method  avoids  exposing  the  baryta  to  the  atmosphere  and  the 
breath  of  the  worker. 

The  above  method,  in  which  the  air  is  collected  in  a  large 
bottle,  is  preferable  to  the  method  of  slow  aspiration  of  air 
through  barium  hydroxide  contained  in  tubes,  for  it  is  more  con- 
venient in  practice,  and  the  sample  represents  the  state  of  the 
air  at  a  particular  time ;  whereas  by  the  latter  method  the  air  is 
being  continuously  collected  for  an  hour  or  more. 


iS6 


LABORATORY   WORK 


Letts  and  Blake  have  pointed  out  that  the  action  of  the 
BaHaOo  on  the  glass  leads  to  a  slight  contamination  with  alkalies 
and  silica,  and  therefore  some  error  of  experiment.  They  recom- 
mend that  the  air-jar  and  the  barjla  stock  bottle  should  therefore 
be  coated  with  paraffin  wax;  but  the  \\Titer  finds  that  this  pre- 
caution may  be  disregarded  in  the  case  of  bottles  which  have 
been  previously  well  exposed  to  BaHgOg. 

The  Process  of  Lunge  and  Zeckendorf  is  quicker  and  simpler 
but  not  so  precise  and  reliable  as  Pettenkofer's,  and  it  is  least 
satisfactory  where  the  amount  of  CO2  is  very  low;  but  it  is  a 
useful  means  of  readily  making  a  closely  approximate  estimation. 

In  this  method  a  decinormal  solution  of  sodium  carbonate  is 
prepared  (5-3  grammes  of  anhydrous  carbonate  to  the  litre),  to 


FIG.    26. — THE   APPARATUS    FOR    THE    LUNGE    AND    ZECKENDORF   PROCESS. 

which  a  little  phenolphthalein  is  added,  a  purple  solution  resulting 
which  keeps  well. 

A  small  caoutchouc  bag  of  70  c.c.  capacity,  and  fitted  with 
two  valves  working  opposite  to  each  other  (so  that  on  pressing 
it  the  air  is  forced  in  one  direction  onlv),  is  connected  by  means 
of  an  india-rubber  tube  with  a  glass  tube,  and  this  passes  through 
a  perforation  in  an  india-rubber  stopper  fitted  tightly  into  a 
small  flask  of  150  c.c.  capacity.  The  ball  is  first  pressed  several 
times,  so  as  to  fill  it  and  the  bottle  with  the  air  to  be  tested; 
2  c.c.  of  the  decinormal  soda  solution  are  then  added  to  100  c.c. 
of  freshl}^  distilled  ammonia-free  water,  and  10  c.c.  of  this  -g^ 
normal  solution  are  emptied  into  the  small  flask. 

The  ail  of  the  bag  is  then  slowly  pressed  over  into  the  reagent, 
the  flexible  tube  is  tightly  compressed  with  the  fingers,  and  the 
flask  well  shaken.  This  is  repeated  with  another  bagful  of  air, 
and  so  on  until  the  purple  colour  is  discharged. 


C.\RB0NIC   ACID 


187 


Lunge  found,  by  direct  experiment,  the  percentage  amount 
of  carbonic  acid  which  corresponds  to  the  number  of  times  the 
air-content  of  the  ball  must  be  discharged  into  the  bottle.  His 
table  is  as  follows: 


Number  of 
Pressures  of  India- 
rubber  Ball. 


7 

0-135 

8 

0-115 

9 

O'lO 

10 

O'og 

II 

0-087 

12 

0-083 

13 

o-o8 

14 

0-077 

15 

0-074 

Parts  per  Cent,  of 

Carbonic  Acid 

in  the  Air. 


0-30 
0-25 
0-21 
0-18 
0-155 


Number  of 
Pressures  of  India- 
rubber  Ball. 


16 

17 
18 

19 
20 
22 
24 
26 
28 
30 

35 
40 


Parts  per  Cent,  of 

Carbonic  Acid 

in  the  Air. 


0-071 

0-069 

0-066 

0-064 

0-062 

0-058 

0-054 

0-051 

0-049 

0-048 

0-042 

0-038 

0-030 


As  suggested  by  S.  H.  Davies,  a  pump  delivering  50  c.c.  per 
stroke  is  better  than  the  caoutchouc  bag  employed  by  the  authors 
of  the  process. 


Haldane's  Rapid  Method  of  Determining  Carbonic 
Acid  in  Air. 
In  this  process  the  apparatus  shown  in  Fig.  27  is  required. 
The  gas  burette  A,  which  is  enclosed  in  a  water-chamber,  consists 
of  a  wide  ungraduated  and  a  very  narrow  graduated  portion. 
It  holds  about  20  c.c.  from  the  tap  to  the  bottom  of  the  scale. 
The  graduated  part,  which  is  about  4  inches  long,  is  divided  into 
100  divisions,  each  of  which  corresponds  to  xowo^h  part  of  the 
capacity  of  the  burette.  The  lowest  division  is  marked  0,  and 
the  highest  100.  Any  difference  between  a  reading  at  or  near 
zero  and  a  second  reading  is  thus  shown  by  the  scale  in  volumes 
per  10,000. 

In  using  the  apparatus  the  air  is  first  expelled  from  the  gas 
burette  by  opening  the  three-way  tap  B  to  the  outside  and 
raising  the  mercury  bulb  C.  The  tap  is  then  closed,  and  the 
mercury  bulb  replaced  in  its  stand.  On  opening  the  three-way 
tap  again  a  sample  of  the  air  is  drawn  in,  and  the  level  of  the 


1 88 


LABORATORY    WORK 


mercury  falls  to  near  the  zero  mark.  The  tap  is  now  opened 
towards  the  absorption  pipette  D,  which  is  filled  up  to  a  mark 
at  E  with  a  20  per  cent,  potash  solution,  and  the  sample  measured 
vvitli  the  precautions  to  be  described  below.  It  is  then  passed 
over  (by  raising  C)  into  the  absorption  pipette,  the  potash  being 
displaced  into  bulb  I.  The  air  is  dri\'en  backwards  and  forwards 
for  a  minute,  and  then  again  measured  after  the  absorption  of 
the  carbonic  acid.     The  difference  between  the  two  readings 


FIG.    27. HALDANE  S    APPARATUS. 

gives  directly  the  number  of  volumes  of  carbonic  acid  per  10,000 
in  the  sample  of  air. 

It  is  evident  that  the  correctness  of  the  analysis  depends 
entirely  on  the  a\oidance  of  errors  of  various  kinds  in  the  two 
determinations  of  the  volume  of  the  enclosed  air.  Mistakes 
might  be  caused  by  slight  variations  in  the  temperature  of  the 
water,  or  the  pressure  under  which  the  sample  is  measured,  or 
in  the  degree  of  saturation  with  moisture  of  the  sample.  A 
variation  of  o-i°  C.  in  the  temperature  of  the  water  in  the  jacket 


CARBONIC  ACID  189 

would,  for    instance,  unless  corrected,   cause  an  error  of  fully 
4  volumes  per  10,000  in  the  analysis. 

In  order  to  have  a  sharp  index  of  the  pressure  under  which 
the  air  is  measured,  the  level,  not  of  the  mercury,  but  of  the 
potash  solution  in  the  narrow  bore  tubing  of  the  absorption 
pipette,  is  taken  as  the  index  of  pressure.  For  the  first  measure- 
ment, the  level  of  the  potash  solution  is  accurately  adjusted  to 
the  mark  at  E  by  raising  or  lowering  the  mercury  by  means  of 
the  rack-and-pinion  arrangement  shown  in  Fig.  27.  For  the 
second  reading  the  potash  level  is  again  adjusted  in  the  same 
way. 

To  correct  for  variations  in  temperature  of  the  water-jacket 
a  control  tube  G  is  employed,  of  a  size  and  shape  approximately 
the  same  as  the  gas  burette.  The  control  tube  communicates 
with  the  potash  through  the  narrow-bore  glass  tube  H,  and 
before  the  first  measurement  is  made  the  level  of  the  potash  in 
H  is  adjusted  to  the  mark  by  lowering  or  raising  the  reservoir  I, 
which  slides  up  and  down  in  a  loosely  fitting  cork.  At  the 
second  measurement  the  same  precaution  is  taken,  so  that  the 
air  in  the  control  tube  occupies  exactly  the  same  volume  as  at 
the  first  measurement.  As  an  alteration  of  temperature  or  of 
barometric  pressure  would  affect  the  pressure  to  an  equal  extent 
in  the  gas  burette  and  control  tube,  it  is  evident  that  the  adjust- 
ment of  the  level  of  the  potash  reservoir  compensates  exactly 
any  error  which  the  alteration  of  temperature  or  of  barometric 
pressure  would  cause  in  the  reading  of  the  gas  burette. 

Before  the  adjustments  of  the  potash  levels  are  made,  the 
water  in  the  jacket  is  thoroughly  mixed  by  blowing  air  through 
it  by  means  of  the  tube  K.  This  manipulation  is  essential  to  an 
accurate  result. 

In  order  to  obviate  error  due  to  variations  in  the  saturation  of 
the  air,  both  the  burette  and  the  control  tube  are  left  with  a 
little  visible  moisture  inside.  If  the  burette  has  once  been 
wetted  inside,  and  as  much  as  possible  of  the  water  expelled  by 
raising  the  mercury,  it  remains  moist  for  a  very  large  number  of 
analyses,  but  a  little  moisture  should  always  be  visible.  If 
by  any  mishap  potash  should  be  sucked  over  into  the  burette, 
it  and  its  connection  must  be  washed  out  with  dilute  acid  intro- 
duced by  the  tap. 

At  the  end  of  an  analysis  the  taps  must  be  turned  so  as  to  close 
the  communication  between  the  potash  and  the  burette  and 


igO  LABORATORY   WORK 

control  tube:  otherwise  potash  may  be  sucked  in  if  there  is  any 
great  fall  of  temperature  or  rise  of  barometric  pressure. 

1  he  manipulations  required  during  an  analysis  may  be  re- 
capitulated as  follows:  (i)  Open  the  tap  of  the  control  tube  to 
the  air  for  a  moment,  and  then  turn  it  so  as  to  connect  the  con- 
trol tube  and  potash-pressure  gauge.  (2)  Turn  the  tap  of  the 
burette  so  as  to  connect  the  burette  and  the  potash  pipette. 
(3)  See  that  the  level  of  the  potash  alters  sharply  and  about 
equally  in  the  tubes  when  the  potash  reservoir  is  raised.  (4)  Blow 
air  through  the  water-jacket.  (5)  Raise  or  lower  the  potash 
reservoir  till  the  potash  is  exactly  at  the  mark  in  tube  H. 
(6)  Raise  or  lower  the  mercury  reservoir  by  means  of  the  rack 
and  pinion  till  the  potash  in  E  is  exactly  at  the  mark.  (7)  Read 
off  the  mercury  level  on  the  scale  of  the  burette  to  0"2  of  a  division. 
(8)  Raise  the  mercury  to  the  upper  hook,  so  as  to  drive  the  air 
into  the  potash  bulb,  then  lower  it  a  little  and  raise  it  again 
twice  so  as  to  \\ash  any  carbonic  acid  in  the  connecting  tubing 
into  the  potash  bulb.  (9)  Return  the  air  to  the  burette. 
(10)  Blow  air  through  the  water-jacket.  (11)  Adjust  the  two 
potash  levels  as  before,  and  read  off  the  mercury  level.  The 
first  reading  subtracted  from  the  second  gives  the  result  in 
volumes  per  10,000.     (12)  Close  the  two  taps. 

The  advantages  of  the  method  are  that  an  estimation  can  be 
made  in  two  or  three  minutes,  only  a  very  small  volume  of  air 
is  required,  and  the  apparatus,  being  fitted  up  in  a  small  box, 
is  exceedingly  portable;  the  disadvantages  are  that  it  is  rela- 
tively costly,  it  only  makes  an  approximate  estimation  of  the 
amount  of  COg,  and  (to  a  beginner)  it  is  rather  difficult  in  manipu- 
lation. The  process  is,  however,  sufficiently  accurate  to  suffice 
for  most  of  the  practical  purposes  of  hygiene. 

Conclusions  to  he  Drawn  from  the  Amount  Estimated. — From  the 
writer's  experiments,  no  "  stuffy  "  odour  is  appreciable  in  the 
atmosphere  until  the  respiratory  impurity  reaches  at  least 
0-03  per  cent,  in  those  cases  where  samples  have  been  collected 
from  rooms  occupied  under  ordinary  conditions. 

This  stuffiness  is  mainly  due  to  exhalations  from  the  skin,  and 
the  degree  of  personal  cleanliness  largely  determines  the  rapidity 
of  its  appearance;  and  recent  experiments  have  demonstrated 
that  the  physical  changes  in  impure  air  are  at  least  mainly  respon- 
sible for  the  ill-effects  of  the  air  of  overcrowded  rooms. 

'Ihese  experiments  included   a  number  of  tests  made  in  a 


CARBONIC   ACID  IQI 

specially  constructed  glass  chamber  in  which  the  physical  and 
chemical  qualities  of  the  air  could  be  rigorously  controlled.  It 
was  found  that  with  a  respiratory  impurity  of  carbonic  acid 
exceeding  any  recorded  up  to  that  time  as  having  been  found  in 
the  air  of  a  crowded  room — e.g.,  from  i-o  to  1-5,  or  even  17  per 
cent. — no  injurious  property  of  the  air  could  be  demonstrated 
so  long  as  the  temperature  and  humidity  were  kept  low;  and 
that  under  these  circumstances  the  absence  of  any  disturbance 
was  so  complete  that  even  the  power  of  cerebration  remained 
intact. 

On  the  other  hand,  as  soon  as  the  temperature  and  humidity 
were  increased  to  beyond  a  certain  point,  there  appeared,  both 
in  normal  and  in  diseased  persons  who  were  submitted  to  experi- 
ment, the  usual  symptoms  that  occur  when  people  are  crowded 
together  in  one  room — i.e.,  feelings  of  discomfort,  oppression, 
lassitude,  giddiness,  nausea,  etc.  These  symptoms,  however, 
could  be  relieved  at  once  by  reducing  the  temperature  and 
humidity  of  the  air  to  normal. 

The  extent  to  which  gas  burned  in  a  common  gas-burner  may 
furnish  carbonic  acid  to  the  atmosphere  is  between  2  and  3  cubic 
feet  per  hour  (for  i  cubic  foot  of  gas  produces  from  0-5  to  o-6  cubic 
foot  of  CO2) ;  and  the  amount  of  sulphur  compounds  thus  yielded 
in  a  gas  well  purified  is  not  important  hygienically. 

The  air  over  burial-grounds,  especially  when  these  are  crowded, 
has  been  said  to  contain  an  abnormally  high  amount  of  carbonic 
acid,  but  the  writer's  experiments  have  failed  to  confirm  this. 


CHAPTER  III 

THE  ORGANIC  MATTER  IN  THE  AIR 

The  organic  matter  in  the  air  includes  that  given  off  from  the 
lungs  and  skin;  its  composition  is  very  imperfecta  understood, 
but  it  consists  partly  of  volatile  fatty  acids  and  their  ethers, 
and  partly  of  vaporous  and  suspended  matters  (epithelial  and 
fatty  debris).  It  is  certainly  largely  oxidizable  and  nitrogenous, 
since  it  will  reduce  solutions  of  the  permanganate  of  potassium, 
and  will  yield  ammonia.  It  quickly  putrefies;  and  when  air 
containing  it  is  aspirated  through  sulphuric  acid,  the  organic 
particles  are  charred  and  darken  the  solution.  When  collected  in 
large  amounts  in  water  it  can  be  precipitated  by  silver  nitrate. 
Probably  the  major  part  is  molecular  and  suspended,  since  it 
does  not  diffuse  equally  about  a  room,  and  tends  to  fall  and 
settle;  and  there  is  no  doubt  that  it  is  mostly  in  combination 
with  watery  vapour,  for  substances  absorb  it  according  to  their 
hygroscopic  powers — i.e.,  it  is  absorbed  chiefly  by  wool,  feathers, 
etc.,  and  least  by  horsehair.  It  gives  a  foetid,  "  stuffy  "  odour 
to  the  atmosphere,  and  from  the  persistence  of  this  odour  it  is 
doubtless  burnt  off  but  slowly  by  the  atmospheric  oxygen ;  and 
in  smaU  quantities  it  gives  odour  to  water. 

The  processes  which  we  may  employ  for  the  estimation  of  this 
matter  in  air  are  preferably  those  which  ser\^e  to  detect  the  same 
matter  in  water.  A  large  measured  volume  of  the  air  is  made 
to  slowly  pass  through  distilled  ammonia-free  water,  which  will 
retain  all  the  soluble  and  suspended  organic  material.  The 
water  is  then  tested  by  Wanklyn's  method  as  to  its  nitrogenous 
organic  matter,  and  by  Tidy's  process,  as  to  its  oxidizable 
organic  matter — it  being  borne  in  mind  in  the  latter  test  that 
either  nitrous  acid,  sulphurous  acid,  sulphuretted  hydrogen,  or 
tarry  matters,  will,  if  present,  also  reduce  permanganate  of 
potassium. 

A  convenient  method  of  performance  (Fig.  28)  is  to  take  a  small 

192 


THE    ORGANIC    MATTER    IN    THE    AIR 


T93 


wash-bottle,  partially  fill  with  250  c.c.  of  distilled  ammonia-free 
water,  and  then  tightly  fit  with  a  doubly  perforated  india-rubber 
stopper.  Into  one  perforation  a  glass  tube  bent  at  right  angles, 
with  one  trumpet-shaped  extremity,  is  accurately  fitted,  while 
the  other  end  is  made  to  dip  well  down  into  the  distilled  water ; 
the  second  perforation  conducts  another  bent  glass  tube,  the  end 
contained  within  the  flask  being  above  the  surface  of  the  water, 
and  the  other  connected  directly  by  india-rubber  tubing  to  a 
second  wash-bottle  similarly  fitted,  and  containing  another 
250  c.c.  of  the  distilled  water.  This  second  bottle  is  connected 
by  india-rubber  tubing  to  the  aspirator.     The  capacity  of   the 


FIG.  28. — -APPARATUS  FOR  COLLECTING  THE  ORGANIC  MATTER  IN  AIR. 

aspirator  being  known  (and  a  convenient  size  is  that  of  20  litres), 
it  is  filled  with  tap  water ;  the  tap  is  then  turned  so  that  the  water 
passes  slowly  out,  when  air  enters  the  trumpet-shaped  mouth  of 
the  bent  glass  tube  to  take  the  place  of  the  escaping  water; 
such  air  is  washed  in  the  distilled  water  in  the  two  bottles  before 
it  reaches  the  aspirator,  and  so  parts  with  its  organic  matter. 

Example.— li  it  is  desired  to  make  an  estimation  of  the  nitro- 
genous organic  matter,  the  aspirator  is  five  times  filled  and  allowed 
to  empty;  100  litres  of  air  will  then  have  been  drawn  through 
the  500  c.c.  of  distilled  water;  therefore  this  500  c.c.  of  water  will 
contain  the  nitrogenous  organic  matter  of  100  litres  of  air. 

13 


194  LABORATORY   WORK 

Suppose,  after  distilling  off  the  free  ammonia,  the  500  c.c.  of 
water  are  found  by  Wanklyn's  method  to  contain  002  milli- 
gramme of  albuminoid  ammonia,  then  there  will  be  002  milli- 
gramme of  such  ammonia  in  100  litres  of  air.  But  in  dealing 
with  air  such  results  are  generally  expressed  in  terms  of  "  milli- 
grammes per  cubic  metre." 

Therefore,  if  there  is  0'02  milligramme  of  albuminoid  ammonia 
in  100  litres,  there  will  be  02  milligramme  of  albuminoid 
ammonia  in  i  ,000  litres — or  a  cubic  metre — of  air. 

Outside  air  contains  albuminoid  ammonia  up  to  ot  milli- 
gramme per  cubic  metre,  and  averages  about  0"o8.  In  a  hospital 
ward  this  ammonia  has  been  estimated  as  high  as  1-3. 

The  oxidizable  organic  matter  may  also  be  collected  in  the 
same  way,  and  estimated  by  Tidy's  process,  as  in  Water  Analysis. 

The  estimation  of  the  oxidizable  organic  matter  can  also  be 
performed  by  very  slowly  aspirating  100  litres  of  air  through 
two  wash-bottles  containing  standard  potassium  permanganate 
solution  and  dilute  sulphuric  acid  kept  at  about  27°  C.  The 
strength  of  the  permanganate  may  be  milHnormal,  as  in  the 
process  next  to  be  described.  In  line,  bright  weather  the  oxi- 
dizable organic  matter  in  town  air  will  absorb  about  3  c.c.  of 
oxygen  per  cubic  metre  or  3  volumes  of  oxj-gen  in  1,000,000 
volumes  of  air,  but  in  stagnant  and  fogg>'  air  the  amount  is 
considerably  higher. 

Another  method  of  approximately  estimating  the  organic 
matter  in  air  is  that  of  Camell}^  and  Mackie.  In  this  process  from 
3  to  4  litres  of  air  are  shaken  with  50  c.c.  of  millinormal  solution 
of  potassium  permanganate  for  five  minutes,  and  the  amount  of 
decomposed  permanganate  is  deduced,  on  colorimetric  principles, 
from  the  loss  in  colour  sustained  by  the  original  solution;  and 
from  the  extent  of  this  loss,  as  estimated  b\'  the  amount  of 
standard  solution  required  to  restore  the  colour,  the  amount  ot 
oxygen  absorbed  can  be  calculated.  One  c.c.  of  the  millinormal 
solution  =0008  miUigramme  0=0-0056  c.c,  at  standard  tem- 
perature and  pressure.  To  each  litre  of  the  17^777  solution  are 
added  50  c.c.  of  dilute  sulphuric  acid  (i  in  6). 

Henriot  and  Bouissy  have  suggested  that  the  moisture  of  a 
measured  volume  of  the  vitiated  air  of  crowded  apartments 
should  be  collected  by  condensation,  and  the  reducing  substances 
estimated  in  the  moisture  obtained. 

The  amount  of  organic  matter  in  air  is  found  to  be  closely 
related  to  the  amount  of  dust. 


CHAPTER  IV 

AMMONIA— MARSH  GAS— CARBON  MONOXIDE— SULPHUR 

COMPOUNDS— NITRIC,  NITROUS  AND  HYDROCHLORIC  ACIDS— 

PHOSPHURETTED  AND  ARSENIURETTED  HYDROGEN 

Ammonia. 
Traces  of  ammonia  are  present  in  every  atmosphere.  In  towns 
it  generally  amounts  to  about  o*o6  milligramme  per  cubic  metre. 
Such  traces  are  derived  almost  entirely  from  the  combustion  of 
coal  and  coal  gas.  The  ammonia  generally  exists  in  combina- 
tion with  an  acid,  as  the  carbonate  and  chloride,  or  less  commonly 
as  the  nitrate  or  sulphate.  Ammonia  may  be  found  in  consider- 
able quantity  near  ground  where  decomposing  organic  matter 
is  deposited.  Traces  of  ammonia  do  not  appear  to  affect  health, 
but  it  is  a  constant  ingredient  of  the  most  impure  airs. 

A  considerable  amount  of  ammonia  in  the  atmosphere  may  be 
detected  by  moistening  strips  of  filtering  paper  with  Nessler's 
reagent,  and  hanging  these  up  for  some  time  in  the  air  of  the  com- 
partment. But  when  present  only  in  faint  traces,  large  quan- 
tities of  air  must  be  aspirated  through  distilled  ammonia-free 
water  rendered  slightly  acid  with  sulphuric  acid,  and  the 
ammonia  tested  for  by  Nessler's  reagent;  and  if  a  measured 
quantity  of  air  is  employed,  the  ammonia  may  be  estimated 
quantitatively  by  "  Nesslerization."  It  has  been  found  as  high 
as  0-8  milligramme  per  cubic  metre  in  certain  hospital  wards. 

Marsh  Gas  (CH4). 

This  gas  probably  exists  in  air  in  many  circumstances,  but 
owing  to  the  difficulties  of  its  detection,  it  is  not  easy  to  prove 
its  presence  when  in  traces  only.  There  are  certainly  traces  in 
the  atmosphere  of  towns,  and  over  districts  of  abundant  vegeta- 
tion (especially  when  such  districts  are  marshy)  it  may  exist  in  con- 
siderable quantities.   As  evolved  from  strata  in  which  coal  mining 

195      • 


iq6  LABORATORY    WORK 

operations  are  progressing  it  is  known  as  "  fire-damp,"  and  its 
power  of  exploding  when  ignited  in  the  presence  of  carbonic  acid 
has  been  often  disastrously  exemplified. 

There  is  little  doubt  that  after  a  while  marsh  gas  may  create 
symptoms  of  poisoning,  and,  being  inodorous  and  non-irritating, 
its  presence  would  not  be  detected  by  the  senses.  Any  escape  of 
coal  gas,  containing  as  it  does  some  35  per  cent,  of  marsh  gas, 
will  charge  the  atmosphere  with  considerable  and  dangerous 
amounts,  but  fortunately  in  these  cases  the  strongly-smelling 
ingredients  of  the  coal  gas  give  timely  warning. 


Carbon  Monoxide  (CO). 

The  affinity  of  this  gas  for  haemoglobin  is  about  three  hundred 
times  greater  than  that  of  ox^-gen.  Owing  to  its  properties  of 
entering  into  combination  with  the  haemoglobin  of  the  red  cor- 
puscles, displacing  their  oxj^gen  and  thus  paralyzing  their 
oxj'gen-carrying  functions,  it  destro^'S  life  by  cutting  off  the 
oxygen  supply  to  the  brain  and  tissues;  and  its  dangers  are 
enhanced  from  the  circumstance  that  it  gives  no  indication  of 
its  presence  to  the  sense  of  odour.  Symptoms  of  poisoning  are 
e\-ident  when  the  haemoglobin  is  about  one-third  saturated  with 
CO,  and  death  results  from  some  70  or  80  per  cent,  of  saturation. 

Sir  T.  Oliver  thus  describes  the  symptoms:  In  acute  intoxica- 
tion the  individual  feels  dizz\',  and  complains  of  headache, 
noises  in  the  ears,  throbbing  in  the  temples,  a  feeling  of  sleepiness, 
and  a  sense  of  fatigue.  There  may  be  a  feeling  of  sickness  which 
culminates  in  vomiting,  a  sense  of  oppression  at  the  chest,  with 
quickened  or  irregular  breathing,  palpitation,  and  an  inability  to 
stand  or  walk  straight.  Convulsions  ma}'  or  may  not  come  on, 
or  there  may  be  only  a  few  muscular  tremors.  There  is  a  peculiar 
fixed  look  about  the  eyes,  the  pupils  of  which  are  dilated  and  their 
reaction  slow.  Consciousness  is  lost  by  degrees,  or  it  may  be 
retained  for  some  time,  and  yet,  owing  to  the  great  loss  of  motor 
power,  the  individual,  although  aware  of  the  danger,  is  often 
unable  to  escape  from  it.  When  a  man  has  recovered  from  the 
effects  of  carbon  monoxide,  his  Ufe  is  still  imperilled  for  some 
days  to  come.  Not  only  does  he  run  the  risk  of  dying  as  late  as 
eight  days  after  the  accident,  but  he  has  still  to  face  the  risk  of 
secondary  maladies  developing — such,  for  example,  as  gl}-cosuria. 

It  may  be  necessary  to  examine  the  air  for  this  gas  in  the 


CARBON    MONOXIDli  I97 

atmosphere  of  compartments  where  iron  or  copper  stoves  are 
employed,  and  especially  when  the  material  is  cast-iron  and  when 
the  fuel  is  coke;  where  coal  gas  (which  contains  some  5-5  to 
6-5  per  cent.,  but  may  contain  from  4  to  12  per  cent.)  is  incom- 
pletely burnt  or  escapes;  or  where  there  is  a  possibility  of  some 
of  the  products  of  combustion  from  leaky  furnace-flues,  etc., 
escaping  into  a  compartment — for  the  air  in  furnace-flues  has 
been  found  to  contain  over  20  per  cent,  of  carbonic  oxide,  and 
that  of  ordinary  flues  from  domestic  fireplaces  as  much  as  4  per 
cent.  The  carbonic  oxide  of  the  air  of  flues  is  always  the  product 
of  imperfect  combustion — that  is  to  say,  the  carbon  is  either 
not  fully  oxidized  to  carbonic  acid  (COg)  owing  to  the  supply 
fresh  air  being  insufficient,  or  else  the  carbonic  acid,  being 
formed  low  down  in  the  furnace,  gets  reduced  to  carbonic  oxide 
in  subsequently  passing  through  the  rest  of  the  furnace. 

Of  the  gases  generated  from  the  explosion  of  gunpowder, 
carbonic  oxide  forms  about  7-5  per  cent.,  but  in  mines  it  is  usually 
only  formed  in  dangerous  amount  by  an  extensive  fire-damp 
explosion,  and  especially  by  an  explosion  in  which  coal-dust  is 
involved. 

A  serious  drawback  to  the  adoption  of  "  water  gas  "  as  a  source 
of  heat  and  light  is  the  fact  that  it  contains  (before  combustion) 
from  25  to  35  per  cent,  of  this  very  dangerous  ingredient. 

Considerable  quantities  of  CO  may  exist  in  the  atmosphere 
near  coke-ovens,  brick-kilns,  and  cement  works. 

The  carbonic  oxide  in  the  atmosphere  of  stove-heated  rooms  is 
derived  from  either  or  several  of  the  following  sources : 

1.  Red-hot  cast-iron  may  transmit  the  gas  from  the  fire,  either 
through  its  substance  or  through  minute  fissures,  and  the  hot 
iron  may  even  reduce  CO2  to  CO.  , 

2.  The  carbon  which  enters  into  the  formation  of  the  cast-iron 
may  get  oxidized,  and  reach  the  external  atmosphere,  as  CO. 

3.  Particles  of  suspended  organic  matter  in  the  atmosphere 
may  get  charred  and  partially  oxidized  by  coming  in  contact 
with  a  highly  heated  stove. 

4.  Currents  may  pass  down  the  smoke  flue  under  certain  con- 
ditions, and  thus  introduce  the  gas. 

In  the  Lancet  of  February  7,  1914,  a  useful  means  of  testing 
as  to  whether  the  products  of  combustion  of  a  gas  stove  are  or 
are  not  entering  a  room  is  described.  When  traces  of  chloroform 
or  carbon  tetrachloride  are  introduced  into  the  mixture  of  air 


198 


LABORATORY    WORK 


and  gas  drawn  into  a  Bunsen  burner,  the  products  of  combustion 
then  contain  hydrochloric  acid,  which,  although  present  in  small 
proportion,  is  readily  detected  by  the  dense  white  fumes  of  am- 
monium chloride  which  it  forms  in  coming  into  contact  with 
ammonia.  All  that  is  necessary,  therefore,  in  testing  a  gas  fire 
as  to  its  ventilating  function  is  to  place  near  the  air  inlet  of  the 
gas  hre  an  absorbent  substance  (a  chalk  pencil)  containing  carbon 
tetrachloride,  and  then  to  hold  on  a  wire  a  piece  of  sponge  con- 
taining strong  ammonia  solution  at  different  points  along  the 
rim  of  the  canopy  of  the  gas  lire.  Any  leakage  or  escape  of 
combustion  products  is  thus  instantly  indicated  by  the  produc- 
tion of  visible  fumes  of  ammonium  cliloride.  The  advantage 
of  this  test  is  that  any  point  of  leakage  can  be  located  from  a 
gas  fire  fixed  in  position  in  the  house. 
CO  is  present  in  traces  in  tobacco  smoke. 


Qualitative  Tests. 

Vogel's  test  is  suffiiciently  delicate  for  all  practical  purposes. 

Into  a  wash-bottle  100  c.c.  of  distilled  water  are  poured,  and 
then  a  little  defibrinated  blood  is  added  to  the  bottle,  which  is 
afterwards  connected  to  an  aspirator.  At  least  10  litres  of  air 
are  then  drawn  through  the  faintly  reddish  liquid.  The  test  is 
obscured  if  too  much  blood  is  present.  The  bottle  is  then  rolled 
about  for  half  an  hour  and  allowed  to  stand  for  a  short  while, 


C                   I 

- 

F 

1 

ii 

1     I'i^ 

liii 

1"  ^^ 

1 

'if 

r 

1 1!  Ill 

1 
1 

FIG.   29. SHOWING   THE   CHARACTERISTIC   DISPOSITION   OF   THE   ABSORPTION 

BANDS  IN  THE  SPECTROSCOPIC  PICTURE  OF  OXY-  AND  REDUCED  KJEMO- 
GLOBIN. 

The  upper  scale  represents  oxy-hasmoglobin  and  the  lower  reduced 
haemoglobin. 

when  some  of  the  contents  are  removed  and  examined  by  the 
spectroscope. 

Oxy-haemoglobin  shows  two  well-marked  bands  with  sharp 
edges,  in  the  yellow  and  in  the  green  parts,  respectively,  of  the 
solar  spectrum,  both  lying  between  Fraunhofer's  lines  D  and  E. 
The  spectroscopic  appearance  of  hemoglobin  in  combination 
with  carbonic  oxide  is  almost  identical,  but  the  left-hand  band 


CARBON  monoxidp:  ^99 

(at  blue  end)  of  the  carbonic-oxide-hEemoglobin  lies  a  lit^e  nearer 
to  the  right  (yellow  end)  than  in  the  case  of   oxy-ha.moglobm 
and  the  edges  of  the  band  are  not  so  sharply  defined      Ihe 
blood  also  takes  up  a  more  or  less  marked  bright  pmk  or  cherry- 
red  tint,  which  may  also  be  observed  in  the  cadaver. 

Two  drops  of  a  colourless  solution  of  ammonium  sulphide  are 
next  added,  the  bottle  is  well  shaken,  and  the  liquid  is  gently 
warmed  and  re-examined.  If  no  marked  change  m  the  spectro- 
scopic appearance  of  the  fluid  has  ensued,  ^^^^^onic  oxide  hemo- 
globin is  present ;  otherwise  the  ammomum  sulphide  will  deoxi- 
dize or  reduce  the  oxy-ha^moglobin,  and  the  two  bands  will  be 
replaced  by  a  single  broad  band  shaded  off  at  the  borders^  and 
occupying  a  position  almost  intermediate  with  regard  to  the 
oridnal  two  bands.  ,,  . 

Delicate  results  are  obtained  where  the  CO  is  not  oo  small  n 
amount,  by  placing  a  mouse  in  a  wire  cage  and  aUowing  it  to 
breathe  the  air  for  several  hours.  The  mouse  may  be  subse- 
quently drowned  in  its  cage,  and  the  blood  then  examined  by 
the  spectroscope,  to  see  if  the  two  absorption  bands  of  CO- 
hemoglobin  are  present.  A  control  test  may  be  made  fro- 
the  blood  of  a  mouse  which  has  not  been  thus  exposed  to  carbon 

"^^T^Xfhas  devised  a  delicate  chemical  test  for  CO-hemoglobin : 
To  10  cc  of  the  solution  of  blood  he  adds  15  c.c.  of  a  20  per 
cent,  solution  of  potassium  ferrocyanide  and  2  c.c.  of  acetic  acid 
(I  volume  of  glacial  acetic  acid  to  2  volumes  of  water) ;  the  pre- 
cipitate very  soon  becomes  reddish-brown  if  CO-hemoglobm  be 
present,  but  greyish-brown  with  oxyhemoglobin,  the  difference 
slowly  disappearing. 

Chemical  Tests  upon  the  Air. 

I  If  air  is  aspirated  through  a  tube  filled  with  a  solution  of 
paUadium  chloride  (containing  i  milhgramme  of  palladium  and 
2  drops  of  hydrochloric  acid),  a  portion  of  the  paUadmm  is 
reduced  to  the  metallic  state  and  a  dark  precipitate  results. 
After  an  hour's  action  with  frequent  shaking,  the  palladium 
which  has  deposited  owing  to  the  reducing  action  of  the  carbon 
monoxide  may  be  collected  and  ignited  with  the  usual  precau- 
tions- I  gramme  of  metallic  palladium  =0-2624  gramnie  or 
-.10  cc   of  CO      The  air  should  first  be  aspirated  through  lead 


200  LABORATORY   WORK 

acetate  solution,  and  also  through  dilute  sulphuric  acid,  to  remove 
any  SHg  or  NH3  which  may  be  present. 

2.  A  known  quantity  of  the  suspected  air,  freed  from  COa  by 
its  passage  through  potash  bulbs,  is  passed  over  periodic  acid 
contained  in  a  U-tube  kept  at  a  temperature  of  80°  C.  The 
carbon  monoxide,  if  present,  decomposes  the  periodic  acid,  setting 
free  iodine.  From  the  amount  of  liberated  iodine  the  quantity 
of  carbon  monoxide  is  deduced.  The  method  is  accurate,  and 
no  other  element  likely  to  be  present  in  the  atmosphere  will 
reduce  periodic  acid;  but  the  air  should  first  be  freed  from  dust. 

Quantitative  Estimation. 

The  subchloride  of  copper  (made  by  exposing  copper  turnings 
and  the  oxide  of  copper  to  the  action  of  strong  hydrochloric  acid 
— S.G.  1-124)  has  the  property  of  absorbing  CO,  and  advantage 
may  sometimes  be  taken  of  this  fact  to  estimate  the  quantity 
present  by  the  method  of  eudiometry,  where  the  amount  is 
considerable  and  exceeds  o-i  per  cent. 

It  is  necessary  that  the  Og  and  CO,  of  the  air  be  first  removed 
by  means  of  potassium  pyrogallol  mixed  with  a  considerable 
excess  of  potassic  hydrate,  before  the  residual  air  is  slowly 
passed  over  into  a  double  absorption  pipette  charged  with  the 
solution  of  subchloride  of  copper. 

It  is  also  necessary  to  use  an  absorption  apparatus  with  large 
bulbs,  in  order  that  a  good  quantity  of  the  copper  solution  may 
be  employed;  and  time  must  be  allowed,  for  complete  absorption 
takes  place  slowly.  Two  or  three  treatments  should  be  repeated 
until  a  "  constant  reading  "  is  obtained,  to  ensure  that  all  the 
gas  has  been  absorbed.  If  there  is  a  marked  amount  of  carbonic 
oxide  present,  the  loss  in  the  original  volume,  taken  under  the 
same  conditions  of  temperature  and  pressure,  is  appreciable, 
and  represents  the  amount  of  CO;  or  the  cuprous  chloride 
solution  may  be  transferred,  under  suitable  precautions,  and 
boiled  in  vacuo,  and  the  expelled  gas  collected.  Quite  98  per 
cent,  of  the  carbonic  oxide  actually  present  will  be  obtained  by 
the  latter  method. 

The  union  of  cuprous  chloride  with  carbonic  oxide  is  very 
feeble,  and  the  solution  readily  parts  with  the  carbonic  oxide 
to  the  atmosphere  on  shaking.  The  solution  will  also  absorb 
acetylene  and  ethylene. 


CAKBON    MONOXIDE  201 

/.  Haldane's  method  of  testing  for  the  i)resenf:e  and  for  esti- 
mating the  amount  of  carbon  monoxide  is  as  follows: 

For  the  detection  of  CO  he  places  in  a  dry  and  clean  bottle 
about  5  ex.  of  a  dilute  blood  solution,  and  then,  after  aspirating 
some  of  the  suspected  air  through  the  bottle,  stoppers  it  and 
shakes  for  ten  minutes.  During  the  shaking  the  bottle  should 
be  protected  from  light,  which  has  a  most  powerful  dissociating 
action  on  CO-hamoglobin.  On  pouring  out  the  solution  into 
a  test-tube  and  comparing  its  tint  with  that  of  some  of  the 
original  solution  in  another  test-tube,  the  presence  of  the  carbonic 
oxide  is  indicated  by  the  pink  tint  of  the  former. 

To  measure  accurately  the  extent  to  which  blood  is  saturated 
with  CO,  Haldane's  method  depends  upon  the  fact  that  normal 
blood,  when  sufficiently  diluted  with  water,  has  a  yellow  colour, 
whereas  blood  saturated  with  carbonic  oxide  forms  a  pink  solu- 
tion when  similarly  diluted.      A  solution  of  about  i  of  normal 
blood  to  100  of  water  is  made;   also  a  solution  of  carmine,  dis- 
solved with  the  help  of  a  little  ammonia  and  diluted  till  its  depth 
of  tint  is  about  the  same  as  that  of  the  blood  solution.     Two  test- 
tubes  of  equal  diameter  (about  |  inch)  are  then  selected.    Five  c.c. 
of  the  solution  of  normal  blood  are  measured  into  one  of  the  test- 
tubes,  and  a  drop  of  the  suspected  blood  is  placed  in  the  other 
test-tube  and  cautiously  diluted  with  water  till  its  depth  of  tint 
is  about  equal  to  that  of  the  normal  solution.     If  carbonic  oxide 
be  present  in  the  hemoglobin,  a  difference  of  quality  in  the  tints 
of  the  two  solutions  will  now  be  clearly  perceptible.     Carmine 
solution  is  then  added  from  the  burette  to  the  normal  blood,  and 
water  (if  necessary)   to  the  abnormal  blood,  till  the  tints  are 
equal  in  both  quality  and  depth.     The  carmine  is   added  in 
about  0-2  c.c.  at  a  time,  the  points  being  noted  at  which  there  is 
just  too  little  and  just  too  much  carmine,  and  the  mean  taken. 
The  solution  of  abnormal  blood  is  then  saturated  with  coal  gas 
by  thoroughly  shaking  up  with  coal  gas  for  a  few  seconds,  and 
the  addition  of  carmine  to  the  other  test-tube  continued  until 
equality  is  again  established,  the  amount  of  carmine  used  being 
noted.     The  percentage  saturation  of  the  abnormal  blood  with 
CO  can  now  be  easily  calculated,  since  we  know  how  much 
carmine  solution  its  saturation  represented  as  compared  with 
what  complete  saturation  represented. 

The   method  of  calculation  is   illustrated  by   the  following 
example:  To  5  c.c.  of  normal  blood  solution  2-2  c.c.  of  carmine 


202  LABORATORY    WORK 

is  required  to  be  added  to  produce  the  tint  of  the  blood  under 
examination,  and  6-2  c.c.  to  produce  the  tint  of  the  same  blood 
fully  saturated.  In  the  former  case  the  carmine  was  in  the 
proportion  of  2-2  in  7-2,  and  in  the  latter  of  6-2  in  11 -2.  The 
percentage  saturation  (.%')  of  the  hemoglobin  with  carbonic 
oxide  is  therefore  given  by  the  following  proportion  sum: 

6-2       2-2 

:  —    :  :  100  :  x  ; 

II-2     7.2 

X  therefore  =55 -2.  As  the  compound  of  CO  with  haemoglobin 
is  to  a  slight  extent  dissociated  when  the  blood  is  diluted  with 
water,  the  value  found  is  a  little  too  low.  The  corrections  needed 
are  as  follows  :  Add  0-5  if  30  per  cent,  saturation  be  found, 
i-i  if  50  per  cent.,  i-6  if  60  per  cent.,  2-6  if  70  per  cent.,  4-4  if 
80  per  cent.,  10 -o  if  90  per  cent.  Thus,  in  the  above  example, 
we  must  add  1-3,  so  that  the  true  saturation  is  56-5  per  cent. 
In  comparing  the  tints  the  test-tubes  should  be  held  up  against 
the  light  from  a  window,  but  bright  light  should  be  avoided  as 
much  as  possible,  as  it  increases  the  dissociation. 

For  the  detection  and  determination  of  small  percentages  of 
CO  in  air  the  sample  of  air  is  collected  in  a  clean  and  dry  bottle 
of  about  4  ounces  capacity.  The  cork  of  the  bottle  is  removed 
in  the  laboratory  under  a  0-5  per  cent,  solution  of  blood,  and 
about  5  c.c.  of  the  air  allowed  to  bubble  out,  a  corresponding 
volume  of  the  blood  solution  entering.  The  cork  is  then  re- 
placed, covered  with  a  cloth  to  keep  off  the  light,  and  shaken 
continuously  for  about  ten  minutes,  when  the  haemoglobin 
will  have  reached  the  point  of  saturation  corresponding  to  the 
percentage  of  CO  present.  The  solution  is  then  poured  out  into 
a  test-tube,  and  the  saturation  determined  with  carmine  solution 
in  the  manner  described  above.  It  is  evident  that  as  in  eacli 
case  the  saturation  found  corresponds  to  a  definite  percentage 
of  CO  in  the  air,  it  is  easy  to  calculate  this  percentage. 

The  method  furnishes  good  results  with  very  small  percentages 
of  CO,  but  becomes  less  and  less  accurate  as  the  amount  exceeds 
0-2  per  cent. 

Sulphur  Compounds. 

Sulphurous  and  sulphuric  acids,  sulphuretted  hydrogen,  and 
ammonium  sulphide  may  all  be  present  in  the  atmosphere  of 
large  towns,  the  first  two  invariably  so,  in  traces;  the  two  latter 
are,  however,  less  often  appreciable. 


SULPHUR   COMPOUNDS  203 

Is 


The  external  atmosphere  of  towns  obtains  sulphur  compounds 
from  the  combustion  of  coal  and  gas. 

Their  presence  may  be  deleterious  to  health,  and  the  oxy- 
acids  of  sulphur  are  unfavourable  to  vegetation  and  destructive 
to  stone-work  and  mortar,  upon  which  a  scale  of  soluble  calcium 
sulphate  forms. 

Angus  Smith  considered  sulphuretted  hydrogen  "  one  of  the 
most  deadly  of  gases,"  and  held  that,  in  traces  even,  "  it  lowers 
the  tone  of  health." 

Sulphuretted  hydrogen,  in  large  quantities,  has  been  ascribed 
as  the  direct  cause  of  death  among  sewer-men  by  Stevenson, 
Haldane,  and  others.  It  is  certain  that  an  atmosphere  con- 
taining from  07  to  0-8  of  SHg  per  1,000  of  air  is  dangerous  to 
human  Hfe.  The  gas  acts  upon  the  nervous  system,  and  causes 
a  functional  arrest  of  the  respiratory  centre  in  the  medulla. 

Sulphurous  acid  in  large  quantities  appears  to  favour  the 
development  of— even  if  it  does  not  induce— bronchitis,  asthma, 
anemia,  conjunctivitis,  etc.  It  may  be  estimated  by  aspirating 
.  a  known  quantity  of  the  air  through  a  dilute  solution  of  bromine 
in  water,  precipitating  the  sulphuric  acid  thus  formed  by  barium 
chloride  solution,  and  calculating  the  SO2  from  the  amount  of 
BaS04  obtained.  From  10  to  17  milligrammes  per  cubic  metre 
of  air  have  been  estimated  under  the  worst  atmospheric  conditions 
of  London  and  Manchester.  A  cubic  metre  of  air  weighs 
1,293,200  milhgrammes,  and  so  this  amount  represents  from 
o-oo8  to  0-013  part  per  1,000. 

Sulphuric  acid  may  be  collected  by  aspirating  a  large  volume 
of  air  through  distilled  water,  and  the  estimation  may  be  made 
by  precipitating  it  as  BaS04,  as  described  under  Water  Analysis. 
Sulphuretted  hydrogen  and  ammonium  sulphide  may  some- 
times be  detected  by  exposing  to  the  air  strips  of  filtering  paper 
moistened  with  a  solution  of  lead  acetate.  Any  faint  evidence 
of  darkening  about  the  borders  of  the  previously  white  paper 
win  prove  the  presence  of  these  gases  in  the  atmosphere.  If  the 
darkening  is  due  to  ammonium  sulphide,  filtering  paper  moistened 
with  a  solution  of  the  nitro-prusside  of  sodium  will  show 
evidence  of  violet  coloration  if  the  gas  is  present  in  sufficient 
quantity. 

A  quantitative  estimation  of  sulphuretted  hydrogen  may  be 
made  by  aspirating  a  measured  volume  of  air  through  a  little 
freshly   prepared   decinormal   solution   of   iodine   in   iodide   of 


204  LABORATORY    WORK 

potassium,  to  which  some  starch  paste  has  been  added.  The 
operation  is  stopped  as  soon  as  the  solution  becomes  colourless 
(H2S4-T2=  2HI  +  S).  Each  c.c.  of  the  iodine  solution  employed 
X  1 7 ^milligrammes  HjS  in  the  volume  of  air  examined. 

The  vapour  of  CSg  may  be  absorbed  in  a  strong  solution  of 
potash  in  06  per  cent,  alcohol;  the  contents  of  the  flask  are  then 
acidulated  with  a  little  acetic  acid.  A  small  amount  of  calcium 
carbonate  is  next  added,  in  order  to  nearly  neutralize.  The 
faintly  acid  solution  is  then  mixed  with  an  amount  of  water 
similar  to  the  potash  solution  employed,  and  a  little  fresh  starch 
solution  is  added.  A  solution  of  iodine  in  potassic  iodide,  con- 
taining 1-666  milligrammes  iodine  per  litre,  is  then  run  in  until 
a  faint  blue  colour  appears.  Every  c.c.  of  iodine  solution  re- 
quired =  I  milligramme  CS.,  in  the  volume  of  air  examined. 

In  testing  for  hydrochloric,  nitric  and  nitrous  acids,  large 
volumes  of  air  must  be  taken.  The  acids  may  advantageously 
be  absorbed  in  10  per  cent,  pure  soda  lye.  The  amount  of  nitric 
acid  in  the  air  is  very  small.  It  is  most  marked  after  thunder- 
storms and  in  the  air  of  towns.  The  above-mentioned  acids 
may  be  estimated  bv  the  methods  described  in  Water  Analysis. 

Chlorine  and  bromine  may  be  absorbed  in  pure  10  per  cent, 
colourless  solution  of  potassium  iodide  (2C1  +  2KI=  2KCI-1-2I), 
and  the  hberated  iodine  titrated  by  decinormal  sodium  thio- 
sulphate  with  starch  (12-69  milligrammes  1  =  7-99  Br  =  3-54  CI). 

Traces  of  arseniuretted  hydrogen  in  the  atmosphere  may  be 
detected  by  aspirating  air  through  a  solution  of  cuprous  cWoride 
in  hydrochloric  acid,  and  then  causing  it  to  impinge  on  a  paper 
impregnated  with  mercuric  chloride,  the  depth  of  tint  of  the 
yellow  strain  produced  serving  to  indicate  the  amount  of  AsHg 
present. 

Phosphuretted  Hydrogen. — This  gas  has  in  recent  years  been 
shown  to  be  given  off  by  ferro-silicon  (employed  in  the  manu- 
facture of  steel)  when  this  material  is  exposed  to  the  action  of 
water  or  moist  air.  There  is  very  little  danger  from  the  low- 
grade  ferro-silicon,  but  the  danger  is  very  great  in  respect  to 
high-grade  ferro-silicon  containing  about  40  to  60  per  cent, 
sihcon.  The  phosphuretted  hydrogen  is  deri\-ed  from  the 
calcium  phosphide  (CagPa)  impurity  in  the  ferro-silicon,  which  in 
contact  with  water  or  moist  air  is  decomposed  with  the  evolution 
of  PH3  (phosphuretted  hydrogen). 

The  gas  is  intensely  poisonous,  experiments  ha\ing  demon- 


NITRIC,    NITROUS    AND    HYDROCHLORIC   ACIDS  20.5 

strated  a  fatal  effect  on  animals  when  the  air  contains  but 
0-25  per  thousand  of  the  gas. 

To  test  for  the  presence  of  the  gas,  air  may  be  aspirated  over 
filter-papers,  one  moistened  with  a  solution  of  nitrate  of  silver 
and  the  other  with  a  solution  of  the  acetate  of  lead.  If  PH,  is 
present,  the  nitrate  of  silver  filter-paper  is  darkened,  but  not  the 
acetate  of  lead  paper;  while  SHg  darkens  both  papers.  It  is, 
however,  preferable  to  separate  any  SHg  before  testing  the  action 
of  the  air  on  the  AgNOg  paper.  The  amount  of  PH3  may  be 
calculated  by  estimating  the  silver  which  is  thereby  precipitated 
from  a  standard  solution  of  AgNOg  (3Ag=PH3). 

Along  with  PHg  a  relatively  small  amount  of  AsHg  may  be 
liberated  from  ferro-silicon,  and  thus  this  equally  poisonous  gas 
may  also  gain  access  to  the  atmosphere. 

Table  of  the  Amounts  of  Various  Gaseous  Impurities  which  have 

BEEN    SHOWN    TO    INJURIOUSLY    AFFECT   HuMAN    BeINGS. 

{Compiled  from  the  Investigations  of  Lehmann,  Matt,  Gruber,  Ogata,  Fried- 
lander,  etc.) 

Chlorine         . .       ^ 

Bromine         •  •        I 

^    ,        ,.,,.,>..  i.  ..      0-002 — 0-005  per  1,000. 

Carbon  bisulphide  ->  r        . 

Iodine  . .       J 

Phosphuretted  hydrogen! 

Hydrochloric  acid         . .  |-  .  •  .  .      o-oi  — 0'05  ,, 

Sulphurous  acid  . .  I 

Ammonia       .  .  "| 

Sulphuretted  hydrogen  -  . .  . .      0-2     — 0-3 

Carbon  monoxide  ) 

Carbonic  acid  . .  .  .  .  .  30 — 50 


CHAPTER  V 

OZONE— PEROXIDE  OF  HYDROGEN 

Ozone  (O3). 

This  gas  is  an  allotropic  oxygen,  in  which  tlie  molecule  contains 
3  atoms  of  ox3'gen  instead  of  the  2  present  in  ordinary  atmo- 
spheric oxygen.  It  is  a  gas  with  a  peculiar  phosphorous  odour, 
and  possessing  marked  irritating  properties  upon  the  mucous 
membrane  of  the  eyes  and  nose  and  upon  the  respiratory  tract. 
In  nature  it  oxidizes  oxidizable  matter,  and  thus  purifies  air. 
It  is  best  prepared  artificially  by  passing  electrical  discharges 
through  moist  air,  and  hence  it  will  be  readily  understood  that  it 
exists  naturally  in  greatest  quantities  during  and  after  thunder- 
storms, when  it  is  also  generally  associated  with  nitric  and 
nitrous  acids  and  peroxide  of  hydrogen.  The  peroxide  of  hydro- 
gen is  also  a  powerful  oxidizing  agent,  by  parting  with  some  of 
its  oxygen  and  becoming  water  (2H202=2H20-i-02).  Nitrous 
acid  also  parts  with  its  oxygen  with  great  readiness. 

There  are  good  grounds  for  doubting  whether  ozone  ever  exists 
in  air  in  appreciable  quantity,  and  whether  it  ever  exceeds 
I  part  in  700,000.  Certainl}'  most  of  the  observations  of  ozone 
hitherto  recorded  have  included  peroxide  of  hydrogen. 

According  to  Tid)^ — 

1.  Most  ozone  is  found  after  thunderstorms,  and  least  in  damp 
and  foggy  conditions  of  the  atmosphere. 

2.  More  is  found  on  the  coast  than  inland,  especially  when  sea- 
breezes  are  blowing. 

3.  More  is  found  at  high  than  at  low  levels. 

4.  More  is  found  in  country  than  in  town  districts. 

5.  More  is  found  in  wintei  (especially  after  heavy  snowstorms) 
than  in  summer. 

6.  More  is  found  during  the  night  than  the  day,  and  most  at 

dawn. 

206 


OZONE — PEROXIDE    OF    HYDROGEN 


207 


7.  The  western  winds  in  Great  Britain  contain  more  ozone 
than  the  eastern.  Houzeau  points  out  that  the  manifestation 
of  ozone  upon  ozone  papers  is  affected  chiefly  by  the  intensity  of 
the  winds  in  most  cases,  except  where  these  blow  directly  off  the 
ocean. 

8.  It  is  rarely,  if  ever,  found  in  the  air  of  occupied  dwelling- 
rooms. 

Test. — A  test  for  ozone  which  has  been  much  employed  is  that 
of  exposing  to  the  atmosphere  a  white  porous  paper  (filtering  or 
blotting)  previously  soaked  in  a  solution  of  potassium  iodide  and 
starch,  and  allowed  to  dry.  Ozone  will  free  the  iodine,  which  then 
combines  with  the  starch  to  form  the  blue  iodide  of  starch,  and 


FIG.    30. THE 


thus  a  blue  colour  is  created  (O3  +  2KI  +  H20=  2KHO  +  Ig  +  O2). 
The  papers  are  exposed  in  a  cage,  and  observations  are  taken 
at  least  every  twelve  hours.  The  cage  aids  in  protecting  the 
papers  from  direct  sunlight,  dust,  and  rain,  each  of  which  may 
lead  to  a  subsequent  fading  of  the  colour;  it  consists  (Fig.  30) 
of  a  double  cylinder  of  very  fine  wire  gauze;  and  projecting 
downwards  from  the  under  part  of  the  lid  is  a  small  hook,  to 
which  the  ozone  papers  are  attached. 

The  above-mentioned  papers  lead  to  errors  of  estimation  from 
the  following  causes: 

I.  Nitrous  oxide  (N2O3),  peroxide  of  hydrogen  and  chlorine 
(each  of  which  may  also  be  present  from  electrical  discharges 
in  the  atmosphere),  and  some  volatile  organic  acids,   produce 


20S  LABORATOKV    WORK 

similar  results  upon  the  papers,  and  sulphurous  acid  and  sul- 
phuretted hydrogen  tend  to  destroy  the  blue  colour. 

2.  The  freed  iodine  is  partially  volatilized,  and  thus  its  effect 
is  lost,  while  some  of  it  may  return  to  the  potash  and  form  inert 
iodide  and  iodate. 

3.  It  is  impossible  to  get  uniform  conditions—?'.^.,  the  amount 
of  light,  moisture,  temperature,  and  wind  \'ary,  and  make  results 
incomparable;  and  the  purity  and  strength  of  the  starch  vary. 

.1  better  test  (Houzeau)  is  the  Ijluing  of  faintly  reddened  litmus- 
paper  previously  moistened  with  a  i  per  cent,  solution  of  potas- 
sium iodide  and  dried,  when  the  ozone  liberates  the  iodine,  and 
the  alkaline  potash  formed  gives  the  paper  a  blue  tint.  In  the 
absence  of  hydrogen  peroxide,  ammonia  is  the  only  other  gas  in 
the  atmosphere  which  can  produce  the  same  effect,  and,  conse- 
quently, another  piece  of  the  litmus-paper,  not  treated  with 
potassium  iodide,  is  exposed  at  the  same  time.  Then  any 
difference  in  the  shades  of  the  two  papers  must  be  furnished  by 
ozone,  which  can  be  estimated  by  means  of  the  ozonometer. 

Perhaps  the  best  papers  for  general  use  are  those  saturated 
with  a  mixture  of  15  per  cent,  solution  of  KI,  and  a  sufficient 
quantity  of  a  i  per  cent,  alcoholic  solution  of  phenolphthalein  to 
render  the  liquid  opalescent.  These  papers  are  coloured  a  fugi- 
tive red  with  ozone,  while  chlorine,  bromine,  or  nitrous  acid  only 
give  a  blue  or  browTi  coloration  (Arnold  and  Mentzel). 

Ozone  papers  must  be  kept  preser\'ed  from  the  air  in  a  tightly 
closed  bottle,  for  to  air  containing  the  merest  trace  of  ozone  the 
papers  react.  But  immediately  before  using  them  for  test 
purposes  they  should  be  moistened,  and  the  tint  matched  as 
quickly  after  the  test  as  possible.  Hydrogen  peroxide  reacts 
similarly  to  ozone  upon  all  these  papers,  and  any  such  ozone 
estimations  are,  in  consequence,  vitiated  by  this  gas. 

Schone  has  pointed  out  that  ozone  blackens  a  bright  piece  of 
silver  foil,  but  hydrogen  peroxide  has  no  such  effect.  More- 
over, chromic  acid,  whether  in  the  solid  form  or  in  solution,  de- 
composes even  the  most  dilute  peroxide  of  hydrogen,  while  it 
has  no  action  on  ozone. 

Engler  and  Wild  find  that  the  best  test  for  ozone  is  by  means 
of  the  chloride  of  manganese,  which  not  only  yields  an  extremely 
delicate  reaction,  but,  in  consequence  of  its  hygroscopic  character, 
keeps  the  prepared  paper  of  the  requisite  moisture.  Ozone  turns 
such   paper  brown  by  the   formation   of   manganese   dioxide. 


OZONE — Peroxide  of  hydrogen  209 

Hydrogen  peroxide  and  nitrous  acid  have  no  such  effect,  but  since 
ammonia  and  its  carbonate  turn  these  papers  brown,  the  colour 
should  be  further  tested  by  moistening  with  tincture  of  guaiacum, 
when,  if  the  papers  have  been  acted  on  by  ozone,  a  blue  colour 
will  be  developed  even  before  the  brown  has  had  time  to  dis- 
appear; whereas  no  blue  forms  if  the  browning  is  due  to  ammonia. 
The  method  by  which  a  quantitative  estimation  of  ozone 
{i.e.,  "  ozonometry ")  is  usually  made  is  colorimetric.  The 
intensity  of  the  colour  created  by  the  ozone  when  the  prepared 
papers  are  exposed  to  the  atmosphere,  generally  for  two  hours, 
is  matched  against  a  standard  scale  (i  to  10)  of  tints,  each  tint 
having  been  originally  produced  by  exposing  similar  papers  to 
known  amounts  of  ozone.  The  greater  the  movement  of  the  air 
the  greater  the  quantity  brought  to  act  upon  the  paper,  and  hence 
less  quantities  of  ozone  present  in  the  atmosphere  on  windy  days 
may  create  more  colour  than  greater  quantities  on  still  days. 
The  only  way,  therefore,  by  which  an  accurate  comparison  of 
the  ozone  in  different  atmospheres  can  be  made  is  by  lining  a 
dry  glass  tube  with  the  ozone  papers,  and  then  aspirating  similar 
quantities  of  air  through  such  tubes. 

Peroxide  of  Hydrogen. 

H2O2  is  generally  present  in  traces,  but  it  exists  in  con- 
siderable quantities  during  and  after  thunderstorms.  It  has 
been  seen  that  it  has  similar  properties  to  those  of  ozone;  it  may 
be  distinguished,  however,  by  certain  of  the  tests  given  under 
"  ozone,"  and  also  by  the  fact  that  it  is  only  after  the  lapse  of 
several  hours  that  it  reddens  potassium  iodide  paste.  A  good 
test  for  the  presence  of  hydrogen  peroxide  is  the  following:  To 
some  distilled  water  that  has  been  made  to  take  up  the  vapour 
add  a  drop  of  a  i  per  cent,  solution  of  potassium  chromate, 
followed  by  a  little  ether  and  a  few  drops  of  dilute  sulphuric 
acid.  On  shaking,  the  ether  takes  up  the  blue  colour  of  per- 
chromic  acid.     The  test  is  fairly  delicate. 


14 


CHAPTER  VI 

SUSPENDED  MATTER  IN  THE  AIR 

The  nature  of  the  suspended  matter  found  in  the  atmosphere 
must  necessarily  ^■ary  widely  with  the  place  and  the  circum- 
stances of  its  collection;  and  it  would  not  be  going  too  far  to  say 
that  particles  of  ahnost  everything  the  observer  can  see  about  ' 
him  may  be  included.  Obviously,  the  amount  increases 
according  to  the  extent  to  which  the  atmosphere  departs  from 
its  state  of  greatest  purity,  high  mountain  air  on  the  one  hand 
containing  few,  and  low  town  air  containing  many. 

It  is  more  especially  in  factories  and  workshops  that  the 
examination  of  suspended  matters  is  important,  since  both  the 
nature  and  number  of  the  particles  have  been  shown  to  determine 
the  prevalence  of  lung  disease.  These  minute  particles  have  a 
tendenc}^  to  settle  when  the  air  is  still,  and  the  collection  and 
microscopical  examination  of  the  dust  which  settles  in  a  closed 
room  furnishes  a  rough  means  of  qualitati\'e  examination. 

The  Methods  of  Collection : 

Undoubtedly  the  best  method  is  to  aspirate  large  volumes 
(loo  litres)  of  air  slowly  through  small  amounts  (lOO  c.c.)  of  dis- 
tilled water,  placed  in  one  or  two  small  wash-bottles ;  the  bottles 
are  then  connected  together  and  with  the  aspirator  by  rubber 
tubing,  as  shown  in  Fig.  28.  The  waters  may  then  be  mixed  and 
evaporated  to  about  20  c.c,  when  drops  may  be  mounted  and 
examined  by  the  microscope. 

This  method  can  be  made  a  quantitative  one  by  aspirating 
a  measured  quantit}-  of  air  through  one  or  two  w^ash-bottles, 
mixing  the  waters,  and  then  counting  the  number  of  particles  in 
an  aliquot  part ;  or  the  water  may  be  evaporated  to  dryness  in  a 
weighed  platinum  dish,  and  the  weight  of  residue  collected  will  be 
the  weight  of  suspended  matter  in  the  volume  of  air  aspirated, 
and  after   ascertaining  the  loss  on  ignition,  this  may  also  be 


SUSPENDED    MATTER    IN    THE    AIR 


211 


expressed  as  "  volatile  "  and  "  non- volatile."  This  method  is 
the  most  suitable  for  collecting  trade  dusts.  If  lead  dust  is  so 
collected  the  lead  may  be  dissolved  out  from  the  ignited  total 
solids  by  nitric  and  hydrochloric  acids,  diluted,  and  then  esti- 
mated colorimetrically.  The  results  should  be  expressed  in 
terms  of  milligrammes  per  cubic  metre. 

Another  method  is  by  means  of  Pouchet's  aeroscope. 

This  instrument  consists  of  a  vertical  glass  cylinder,  capable 
of  being  hermetically  closed  at  either  end  by  a  copper  ferrule. 
The  ferrule  at  the  upper  extremity  of  the  cylinder  is  a  permanent 
fixture,  and  gives  passage  to  a  vertical  copper  tube  which  is 
partly  outside  and  partly  enclosed  within  the  cylinder;  of  this 
tube  the  extremity  of  the  part  which  is  outside  the  cylinder  is 
expanded  into  a  trumpet-shaped  mouth,  and  the  end  of  the  part 
which  is  inside  the  cylinder  is  gradually  drawn  to  a  very  fine 
point,  not  more  than  0-5  millimetre  in  diameter. 

The  ferrule  at  the  lower  extremity  of  the  cylinder  is  tem- 
porarily removed,  so  that  a  circular  glass  slide — which  has  been 
previously  smeared  with  pure  clean  glycerine — can  be  placed 
with  its  centre  immediately  under  the  finely  drawn  point  of  the 
copper  tube.  The  whole  apparatus  is  then  made  air-tight  and 
connected  with  the  aspirator.  The  air  which  is  thus  sucked  in 
falls  in  a  spray  upon  the  glass  slide,  and  the  glycerine  retains  the 
suspended  matter.  Subsequently  the  slide  can  be  removed  and 
examined  by  the  microscope. 

A  slight  modification  of  Pouchet's  aeroscope  is  the  instrument  of 
Marie  Davy.    The  accompanying  figure  sufficiently  explains  itself- 


FIG.    31. M.    MARIE   DAVYS   MODIFICATION   OF   POUCHET  S    AEROSCOPE. 


.  Hesse's  apparatus  is  seen  by  Fig.  32  to  consist  of  a  long  glass 
tube  connected  at  one  end  to  the  aspirator ;  the  small  india-rubber 
cap  which  closes  the  other  end  is  removed  just  before  use,  and 
50  c.c.  of  pure  glycerine  is  poured  into  the  tube,  which  is  then 


212 


LABORATORY    WORK 


turned  round  so  as  to  make  the  gl}'cerine  coat  the  whole 
interior.  As  the  air  is  subsequently  aspirated  through  the 
tube,  the  suspended  matter  is  caught  up  by  the  glycerine, 
which  can  be  removed  by  a  clean  spatula  and  examined  micro- 
scopically. 

But  methods  in  which  glycerine  is  employed  are  somewhat 
unsatisfactory,  for  the  reason  that  the  original  glycerine  will 
generally  contain  solid  particles.  A  preliminary  microscopic 
examination  of  the  glycerine,  however,  does  not  entail 
much  additional  labour  or  time,  and  thereby  the  nature  and 
amount  of  the  foreign  matter  it  contains  can  be  previously 
noted. 

A  fourth  plan  entails  the  use  of  a  pure  sugar  filter  through 


FIG.  32. HESSE's  apparatus  FOR  THE  COLLECTION  OF  SUSPENDED  MATTERS 

IN    THE   AIR. 

a,  The  extremity  connected  with  the  aspirator;  b,  a  removable  cap. 


which  the  air  is  slowly  drawn;  the  sugar  is  then  dissolved  in  a 
sufficiency  of  pure  water,  when  the  suspended  matters  caught 
up  in  it  are  retained  in  suspension  in  the  water,  and  may  be 
collected  and  examined  microscopically.  The  filter  is  best 
arranged  as  a  glass  tube,  at  least  an  inch  in  diameter,  disposed 
horizontally,  and  packed  (not  too  tightly)  for  se\-eral  inches  with 
the  sugar  crystals.  One  end  of  the  tube  is  left  open  for  the 
entrance  of  air,  and  the  other  connected  by  india-rubber  tubing 
with  an  aspirator.  The  filter  dissolved,  the  suspended  matter 
may  also  be  separated  by  filtration  through  a  weighed  Swedish 
filter-paper,  then  thoroughly  washed  and  dried  at  a  low  tempera- 


SUSPENDED    MATTER    IN    TITE    ATE  2Tf; 

ture  and  woiglicd.  If  tlio  amount  of  air  aspiratcfl  has  l)een 
measured,  the  weighed  quantity  of  its  original  suspcndf^d  matter 
can  be  expressed  quantitatively. 

It  is  obvious  that  the  amount  of  the  dust  in  town  air  must  vary 
considerably;  commonly  the  extent  of  this  variation  is  between 
5  and  25  milligrammes  per  cubic  metre;  it  has  been  estimated 
as  high  as  224  in  cement  works  during  work. 

J.  Aitken  has  devised  an  ingenious  method  of  enumerating 
the  particles  of  suspended  matter  in  the  atmosphere.  A  full 
description  of  the  elaborate  apparatus  may  be  studied  in  the 
Proceedings  of  the  Royal  Society  of  Edinburgh,  1889.  In  this 
method  a  measured  quantity  of  air  is  taken  and  passed  into  a 
receiver,  where  it  is  mixed  with  a  large  measured  quantity  of 
filtered  (dustless)  air,  and  saturated  with  water.  The  air  in 
the  receiver  is  then  expanded  by  means  of  an  air-pump;  a 
shower  of  rain  is  thus  produced  which  carries  down  the  sus- 
pended matter,  and  the  number  of  particles  which  fall  on  a 
measured  area  are  then  counted.  From  10,000  particles  per 
c.c.  of  air  to  over  2,000,000  may  thus  be  obtained  from  the  outside 
air,  and  in  occupied  rooms  near  the  ceiling  they  may  reach  many 
millions.  In  the  centre  of  London  the  average  is  from  about 
250,000  to  500,000  per  c.c,  while  at  the  top  of  lofty  mountains 
and  in  mid-ocean  the  dust  particles  may  number  only  from 
200  to  300.  On  the  Terrace  of  the  House  of  Parhament, 
London,  the  air  was  found  to  contain  about  40,000  particles 
per  c.c. 

Aitken  has  demonstrated  that  it  is  the  dust  in  the  atmosphere 
which  determines  mists  and  fogs,  inasmuch  as  the  condensation 
of  aqueous  vapour  is  not  determined  only  by  reduction  of  tem- 
perature but  also  by  the  presence  of  particles  of  dust,  each 
particle  becoming  shrouded  with  a  covering  of  moisture.  By 
his  method  of  enumeration  it  is  assumed  that  each  droplet  has 
for  its  nucleus  a  dust  particle. 

Vomer  employs  a  blackened  resinous  substance  which  on  cool- 
ing presents  a  uniform  and  polished  surface.  This  surface  may 
be  protected  from  dust  access  prior  to  the  experiment  by  means 
of  a  watch-glass  sealed  down  with  vaseline.  For  the  purpose  of 
an  experiment  the  watch  -  glass  is  removed  and  an  exposure  of 
ten  minutes  is  made;  when,  by  means  of  an  electric  lamp, 
the  number  of  dust  particles  per  square  centimetre  may  be 
counted. 


214  LABORATORY   WORK 

Dust  collected  from  the  top  of  a  wardrobe  in  a  bedroom 
yielded  the  following  results  on  analysis: 

]\Ioisture    ....          .  .          .  .          . .  4-4 

Organic  matter    . .          . .          .  .          .  .  52'6 

Silica  and  insoluble  silicates      ..          ..  21-0 

Oxide  of  iron  and  alumina                    .  .  97 

Lime  (CaO)          6-2 

Carbonic  acid,  witli  traces  of  sulphuric 

and  phosphoric  acid    .  .          .  .          .  .  Tvi 


TOO-O 


The  inorganic  mattei  was  mostly  amorphous,  wliile  the  organic 
was  for  the  most  part  organized.  Among  the  commonest  con- 
stituents of  the  latter  were  vegetable  and  animal  fibres  derived 
from  fabrics,  such  as  linen,  cotton  and  wool.  In  addition  there 
were  a  few  feather  barbs  and  particles  of  carbon ;  squamous 
epithelial  cells  from  the  skin,  starch  granules,  and  a  few  pollen 
spores  were  also  identified. 

The  dust  from  20  square  yards  of  glass  roofs  at  Kew  and 
Chelsea  was  found  to  contain  nearly  5  per  cent,  of  SO3.  equal 
to  about  2  per  cent,  of  S. 

The  soot-fall  from  the  atmosphere  over  industrial  centres  can 
be  estimated  by  collecting  it  in  a  hopper  of  known  collecting  area, 
which  terminates  below  in  a  small  tube  connected  with  a 
capacious  bottle.  The  apparatus  is  similar  to  a  rain-gauge,  and 
it  collects,  of  course,  both  rainfall  and  deposit.  It  has  been 
found  that  in  the  city  area  of  London  some  650  tons  of  soot  fall 
upon  every  square  mile  each  year.  There  are  marked  differences 
between  domestic  and  boiler  soot.  The  latter  is  little  more  than 
dust  or  ash,  practically  all  the  hydrocaibons  having  been 
burnt;  whereas  the  former  possesses  a  high  content  of  tar  and 
volatile  substances  and  a  low  content  of  ash. 

The  Nature  of  the  Suspended  M.vtter  of  Air. 

The  following  substances  may  be  found: 

Animal. — Debris  from  wear  and  tear  of  clothes,  etc. ;  wool 
and  silk  fibres  ;  human  hair  ;  particles  of  feather  ;  debris 
of  dried  epithelial  cells,  and  epidermic  scales  from  skin; 
fragments  of  insects — i.e.,  scales  from  wings,  legs;  particles 
of    the    spider's    web  ;     dried    faecal    particles    from    horses' 


SUSPENDED    MATTEK    IN   THE    AIR  215 

dejecta;   minute  ova;  amnebifoim  organisms;   mohjcular  debris 
in  considerable  quantity. 

Vegetable.  —  Particles  of  carbonaceous  matter  ("soot"); 
molecular  debris  in  large  quantity;  vegetable  fibres,  hairs  and 
cells;  cotton  and  linen  fibres;  starch  grains;  portions  of  plants, 
and  pieces  of  woody  fibre;  pulverized  straw;  moulds,  fungi, 
diatoms,  and  bacteria  and  their  spores;  pollen  grains;  algae, 
notably  Protococcus  -pluvialis  and  also  the  small  oval  cells  of 
other  unicellular  algai.  The  spores  and  mycelium  of  A  chorion 
Schonleinii  and  Tricophyton  tonsurans  have  been  found  in  the 
atmosphere  of  skin  wards. 

Mineral.- — Especially  numerous  when  the  ground  is  dry. 
Minute  particles  of  every  chemical  constituent  of  the  soil  may  be 
raised  up  into  the  atmosphere — e.g.,  silica,  silicate  of  alumina 
chalk,  peroxide  of  iron,  etc.  Sodium  chloride  is  invariably 
present,  and  is  in  greatest  quantities  at  the  seaside.  Lead, 
arsenic,  and  zinc  may  be  furnished  by  the  wall-papers,  paint, 
and  "  dryers"  employed  upon  the  walls  of  rooms;  arsenic  also 
from  artificial  fruit,  flowers,  curtains,  etc.,  used  for  ornamenta- 
tion; coal  dust,  etc. 

There  are  certain  trade  dusts  which  vitiate  the  air  of  the 
immediate  neighbourhood  in  which  the  trade  processes  are 
carried  on;  and  particles  of  a  great  variety  of  substances  may 
thus  find  their  way  into  the  atmosphere  from  coal,  tin,  stone, 
slate,  cement,  wood,  clay,  steel,  flour,  textile  fabrics,  glass,  etc.; 
while  poisonous  matter  may  get  into  the  atmosphere  where  lead, 
arsenic,  copper,  chromium,  phosphorus,  and  mercury  are  being 
used  for  trade  purposes. 


CHAPTER  Vll 

THE  CHARACTERS  OF  THE  AIR  COLLECTED   FROM  VARIOUS 
SOURCES— BACTERIOLOGICAL  NOTE 

Marsh  Air. 
The  air  collected  over  marshy  regions  is  contaminated  by  the 
products  of  \'egetable  decomposition. 

Such  air  contains  excess  of  carbonic  acid,  commonly  0-05  per 
cent.;  marsh  gas  may  be  markedly  present;  sulphuretted 
hydrogen  is  also  sometimes  appreciable ;  watery  vapour  in  large 
amount;  ammonia  in  traces;  phosphuretted  hydrogen  in  faint 
trace.  The  suspended  matter  is  found  to  mainly  consist  of  vege- 
table debris,  algse,  diatoms,  fungi,  and  other  micro-organisms. 

In  many  cases  where  the  presence  of  sulphuretted  hydrogen  is 
appreciable  the  marshy  waters  contain  soluble  phosphates,  which 
become  deoxidized  to  sulphides  by  reducing  agents  (chiefly 
organic  matter) ,  and  the  sulphuretted  hydrogen  doubtless  results 
from  the  action  of  vegetable  acids  upon  these  sulphides. 

Sewer  Air. 

Sewer  air  varies  in  composition  with  the  sewage  and  the  state 
of  the  sewerage  system.  Its  reaction  is  generally  alkaline. 
Its  temperature  practically  never  falls  below  9°  C,  and  it  is 
always  saturated  with  moisture,  or  nearly  so. 

Oxygen  is  variously  diminished,  according  to  the  efficiency  of 
the  sewer  ventilation;  it  is  sometimes  in  normal  proportions. 

Carbonic  acid  is  variously-  increased  from  the  same  cause;  it 
probablv  does  not  average  in  a  good  modern  system  of  sewerage 
more  than  three  times  the  amount  normal  to  the  atmosphere, 
but  it  may  be  ten  times  as  great,  or  even  more. 

Ammonia  is  somewhat  in  excess  of  the  external  air,  and  it 
may  be  greatly  in  excess. 

216 


SEWER   Airs.  2T7 

Sulphuretted  hydrogen  ^  may  be  present  in  variable  quantities. 
Ammonium  sulphide       -  but  usually  only  in  traces.     If,  how- 
Carbon  bisulphide  J  ever,    the  sewage    stagnates    in    the 
sewer,  the  sulphuretted  hydrogen  may  be  present  in  consider- 
able amount.     Marsh  gas  is  in  traces,  or  absent;  and  traces  of 
nitrous  dioxide  and  phosphuretted  hydrogen  may  be  present. 

The  fcetid  and  putrid  organic  vapours  of  sewage  are,  according 
to  Odling,  aUied  to  the  compound  ammonias,  and  are  probably 
carbo  -  ammoniacal  and  contain  traces  of  animal  alkaloidal 
substances. 

The  odour  of  sewer  air  is  not  usually  due  to  sulphuretted 
hydrogen,  but  to  minute  quantities  of  a  variety  of  volatile 
substances,  such  as  indol,  skatol,  the  mercaptans,  and  com- 
pound ammonias. 

The  micro-organisms  are  almost  exclusively  moulds  and 
micrococci,  and  these,  together  with  animal  and  vegetable 
debris,  appear  to  constitute  the  very  sparse  suspended  matter. 
The  micro-organisms  in  the  sewer  air  are  related  more  to  the 
micro-organisms  in  the  air  outside  than  to  those  of  the  sewage 
(Andrewes  and  Law) ;  they  are  generally  fewer  in  number  than 
those  of  the  outside  air  at  the  same  time.  Splashing  may, 
however,  disseminate  sewage  bacteria  in  sewer  air,  and  possibly 
also  the  bursting  of  bubbles  or  the  ejection  of  minute  droplets 
from  flowing  sewage  (Haldane,  Carnelly,  Horrocks,  Andrewes). 

The  organic  matter  in  sewer  air  probably  averages  from  two 
to  three  times  the  amount  in  the  outside  air. 

The  Air  in  Coal  Mines. 

The  oxygen  is  diminished,  and  the  reduction  may  be  extremely 
faint  or  so  considerable  that  the  total  oxygen  does  not  much 
exceed  i8  per  cent.  The  carbonic  acid  is  increased,  and  may 
reach  1-5  per  cent,  or  over.  A  trace  of  carbon  monoxide  is 
generally  present.  The  considerable  variations  in  the  amounts 
of  oxygen  and  carbonic  acid  in  different  mines  are  mainly  de- 
pendent upon  the  ventilation  provided.  Marsh  gas  is  sometimes 
in  large  amount,  but  it  may  be  only  in  traces  in  some  mines. 
A  little  sulphuretted  hydrogen  may  be  present,  and  in  some 
mines  high  percentages  of  "  black  damp  "  or  "  choke  damp  " 
get  into  the  atmosphere.  "  Black  damp  "  is  a  mixture  of 
nitrogen  with  a  relatively  small  proportion  (generally  from  10  to 
15  per  cent.)  of  carbonic  acid. 


21 8  LABORATORY   WORK 

Tlie  marsh  gas,  or  methane,  mav  be  estimated  in  the  following 
manner:  The  volume  of  carbonic  acid  present  in  a  sample  of 
the  air  is  first  determined  by  absorption  in  a  lo  per  cent,  solution 
of  caustic  potash,  then  the  methane  is  burnt  bj^  passing  the  air 
to  and  fro  over  a  spiral  of  incandescent  platinum  wire.  The 
contraction  resulting  from  the  combustion  of  methane  is  exactly 
double  the  CO2  formed.  Methane  on  combustion  produces  its 
own  volume  of  carbonic  acid;  and  the  carbonic  acid  so  produced 
may  be  absorbed  in  the  solution  of  caustic  potash,  and  its  volume 
thus  measured.  The  contraction  on  combustion  and  the  volume 
of  carbonic  acid  formed  would  bear  a  different  ratio  to  one 
another  if  the  combustible  gas  were  any  other  than  methane. 

For  useful  particulars  of  mine  air  anaJyses  the  reader  should 
consult  "  Methods  of  Air  Analyses,"  by  J.  S.  Haldane,  M.D., 
F.R.S. 

Town  Air  during  Fogs. 
Reactibn  acid;  oxygen  is  slightly  diminished;  carbonic  acid 
very  much  increased — may  even  exceed  0-09  per  cent. ;  sul- 
phurous acid  and  sulphuric  acids  markedly  present;  carbon 
bisulphide  in  traces;  maybe  carbonic  oxide,  ammonia,  am- 
monium sulphide  or  carbonate  in  traces;  sulphuretted  hydrogen 
generally  in  faint  traces;  watery  vapour  excessive;  fine  sus- 
pended particles  of  carbon  and  tarry  matters,  together  with  an 
increase  of  the  commoner  form  of  suspended  matter  in  air. 

Ground  Air. 

Ground  air  mav  be  drawn  from  considerable  distances  into 
a  house,  especially  during  periods  of  frost,  owing  to  the  aspirat- 
ing effect  of  the  warmed  and  expanded  air  of  the  house  itself; 
and  the  foul  air  of  a  leaky  drain  or  cesspool  may,  under  favour- 
able circumstances,  be  sucked  through  the  earth  into  a  dwelling 
for  a  distance  of  many  yards.  When  it  is  borne  in  mind  that 
many  houses  contain  cellars  built  and  ventilated  considerably 
below  the  ground  level,  it  will  be  realized  that  "  ground  air" 
must  enter  materiallv  into  the  constitution  of  the  atmosphere 
of  such  cellars. 

Ground  aii  contains  an  enormously  high  percentage  of  car- 
bonic acid,  and  the  maximum  amount  of  this  impurity  is  always 
found  between  July  and  November,  when  the  prevalent  tem- 
perature   and     moisture    favour    the    rapid    decomposition    of 


GROUND    AIR 


219 


vegetable  matter.  The  ground  air  of  sandy  soils  contains 
relatively  little  COg. 

Ground  air  commonly  contains  traces  of  ammonia,  sulphuretted 
hydrogen,  and  hydrocarbons.  It  is  very  free  from  micro- 
organisms. The  CO2  increases  with  the  depth  of  the  soil  and 
it  is  sometimes  as  much  as  5  per  cent,  in  deep  soil  a  few  feet  from 
the  surface. 

The  entrance  of  ground  air  into  ground-floor  rooms,  base- 
ments and  cellars  may  be  detected  by  comparing  the  carbonic 
acid  found  in  these  rooms  with  that  in  the  external  atmosphere, 
when  any  considerable  excess  of  this  gas  (not  otherwise  accounted 
for)   points  to  such  pollution.     The  source  of  other  impurities 


v- 


8— --- 


FIG.    33. HESSE  S    APPARATUS    FOR    COLLECTING    GROUND    AIR. 

present  may  also  be  traced  by  collecting  samples  of  the  ground 
air  in  the  vicinity  of  the  house  and  comparing  the  results  of  such 
examination. 

A  sample  of  ground  air  may  be  conveniently  taken  in  the 
following  manner:  A  sharp-pointed  narrow  steel  cylinder,  with 
numerous  perforations  just  above  its  point,  is  driven  into  the 
earth  to  depths  varying  from  i  to  4  feet.  The  upper  end  of  the 
tube  is  connected  with  a  large  air-jar,  which  is  again  connected 
to  an  aspirator.  The  connection  between  the  jar  and  the  steel 
cylinder  is  shut  off,  and  the  jar  is  first  emptied  (by  means  of  the 
aspirator)  of  the  air  it  contains  ;  the  connection  is  then  re- 
established and  the  sample  collected  by  aspiration. 


220  LABORATORY    WORK 

Bacteriological  Note. 

Bacteria  are  always  present  in  air,  but,  unless  the  air  con- 
tains a  large  number  of  dust  particles,  in  comparatively  scanty 
numbers. 

The  determination  of  the  number  of  organisms  is  of  greatest 
use  as  a  means  of  comparing  methods  of  ventilation.  Pathogenic 
organisms  are  not  readily  detected  in  air,  the  organisms  usually 
found  being  moulds  and  saprophytic  bacteria. 

Fliigge  has  shown  that  in  inhabited  rooms  the  air  is  liable 
to  be  contaminated  with  bacteria  derived  from  the  presence  of 
droplets  of  mucus  extruded  from  the  buccal  cavity  in  the  acts 
of  sneezing,  coughing,  and  loud  speaking. 

Gordon  has  greatly  extended  our  knowledge  of  such  particulate 
pollution,  and  has  shown  that  certain  bacteria,  which  can  be 
detected  and  estimated,  furnish  means  whereby  these  different 
kinds  of  pollution  can  be  recognized. 

According  to  Gordon,  pollution  of  three  separate  kinds  can 
be  recognized  by  bacterial  tests. 

1.  Pollution  from  Material  derived  from  the  Uj)per  Respiratory 
Passages. — Gordon  has  shown*  that  certain  streptococci  are 
present  in  enormous  numbers  in  human  sali\\a,  and  tliat  their 
presence  serves  as  a  means  whereby  the  addition  of  saliva  to  air 
can  be  detected.  The  organism  specially  characteristic  of  such 
pollution  is  the  Streptococcus  salivarius. 

2.  Pollution  from  Material  detached  from  the  5Am.— The 
Staphylococcus  epidermidis  albus  is  constantly  present  on  the 
human  skin,  and  by  its  detection  in  air  the  presence  of  particles 
detached  from  the  skin  may  be  deduced. 

3.  Pollution  by  Material  brought  in  from  the  Street  on  Boots. — 
Such  material  consists  largely  of  horse-dung,  and  may  be  recog- 
nized by  the  presence  of  B.  coli,  spores  of  B.  enteritidis  sporogenes 
and  Streptococcus  equinus. 

*  Local  Government  Board,  Medical  Ofiiccr's  Report,  1902-03,  p.  4 


CHAPTER  VIII 

SCHEME  FOR  THE  DETECTION  OF  GASES  WHEN  PRESENT  IN 
LARGE  QUANTITIES 

Whereas  for  the  detection  of  various  gases  whicli  may  con- 
taminate tlie  atmosphere  it  is  necessary  to  pass  large  volumes 
of  air  through  distilled  ammonia-free  water  containing  agents 
with  which  tlie  gases  will  combine,  and  then  to  apply  the 
necessary  tests,  yet,  when  these  gases  exist  in  considerable 
quantities  (as  in  the  atmosphere  of  chemical  manufactories,  or 
those  manufactories  in  which  chemicals  are  employed),  they 
may  often  be  discovered  by  tests  applied  to  small  quantities  of 
the  air  collected  in  air-jars. 

1.  Moisten  two  pieces  of  delicate  red  and  blue  litmus-paper 
in  neutral  distilled  water,  and  catch  these  between  the  stopper 
and  the  neck  of  the  bottle  in  such  a  way  that  they  hang  down 
into  the  bottles  free  of  the  sides.  Note  any  change  in  the  colour 
of  these  papers  after  waiting  two  or  three  minutes. 

2.  If  the  reaction  is  acid  or  alkaline  pour  rapidly  into  the  jar 
a  small  quantity  of  distilled  ammonia-free  water  {i.e.,  about 
10  c.c),  and  replace  the  stopper  at  once;  then  shake  vigorously, 
so  that  some  of  the  gas  may  be  taken  up  by  the  water. 

A.  //  the  blue  litmus-paper  turns  red  {i.e.,  the  gas  is  acid),  it 
is  either  carbonic  acid,  hydrochloric  acid,  sulphurous  acid,  nitric 
or  nitrous  acid. 

Add  a  drop  or  two  of  a  solution  of  silver  nitrate  to  some  of  the 
water  poured  from  the  air- jar  into  a  test-tube. 

{a)  A  white  precipitate  denotes  the  presence  of  either — 

I.  Carbonic  Acid. — Very  slight  precipitate,  insoluble  in  nitric 
acid;  acidity  also  very  faint.  Clear  baryta  water  added 
to  the  jar  becomes  turbid  after  shaking,  and  the  tur- 
bidity is  increased  by  adding  ammonia. 


222  LABORATORY    WORK 

2.  Hydrochloric  Acid. — Marked  precipitate,  insoluble  in  nitric 

acid,  but  soluble  in  ammonia  and  potassium  cyanide; 
acidity  also  marked. 

3.  Sulphurous   Acid. — Marked   precipitate,    soluble   in   nitric 

acid;  the  precipitate  on  being  heated  clears  up  and  the 
solution  darkens  (AggS).  The  water  from  the  jar  will 
decolorize  iodide  of  starch  solution;  and  if  it  be  warmed 
after  the  addition  of  hydiochloric  acid  and  zinc,  a  piece 
of  lead  acetate  paper  held  over  the  test-tube  becomes 
darkened  (S02  +  3H2=  SH2  +  2H2O).  Odour  character- 
istic. 

{b)  There  is  no  precipitate,  and  this  fact  denotes  the  presence 
of  either — 

1.  Nitric  Acid. — Add  brucine  and  sulphuric  acid  to  some  of  the 

water  from  the  jar,  and  note  the  appearance  of  the  pink 
zone  changing  to  yellow  and  brown;  or  add  a  crystal  of 
ferrous  sulphate  and  then  sulphuric  acid  to  the  water, 
and  note  the  brown  coating  of  the  green  crystal. 

2.  Nitrous  Acid. — Add  a  drop  of  a  solution  of  starch  and 

potassium  iodide,  and  then  a  drop  of  sulphuric  acid.  A 
blue  colour  forming  at  once  denotes  the  presence  of  this 
acid ;  or  the  Ilosva}^  test  may  be  applied. 

B.  If  the  red  paper  is  turned  blue  {i.e.,  the  gas  is  alkaline), 
it  is  either — 

1.  Ammonia. — Add  a  drop  or  two  of  Nessler's  reagent  to  a 

Uttle  of  the  water  from  the  jar,  when  a  yellow  to  orange 
colour  appears.     Odour  characteristic. 

2.  Ammonium    Sulphide. — Nessler's   reagent    causes    a   black 

colour  to  appear  when  added  to  some  of  the  water  from 
the  jar;  and  a  solution  of  nitro-prusside  of  sodium  pro- 
duces a  violet  colour.  Odour  characteristic — i.e.,  that 
of  rotten  egg  predominates,  but  it  is  easy  also  to  detect 
the  presence  of  ammonia. 

C.  //  the  litmus  is  not  affected   {i.e.,   the  gas   is  apparently 
neutral),  it  may  be — 

Sulphuretted  Hydrogen. — Lead  acetate  papers  placed  in  the 
jar  are  darkened,  as  are  also  solutions  of  lead,  iron,  or 
copper  salts.      Odour  characteristic. 


IDETECTION    OF   GASES  223 

D.  //  the  litmus-pap^.vs  are  firsL  reddened  and  then  slowly 
bleached,  the  gas  is — 

Chlorine. — Filtering  paper  moistened  in  a  solution  oi 
potassium  iodide  and  suspended  in  the  jar  is  first  dark- 
ened by  liberated  iodine  and  then  bleached.  Odour 
characteristic.  Furnishes  a  red  colour  with  a  mixture 
of  sulphocyanide  of  potassium  and  a  proto-salt  of  iron. 

Note.' — Sulphuretted  hydrogen  has  many  reactions  in  common 
with  ammonium  sulphide — e.g.,  both  gases  will  darken  lead 
acetate  papers  and  solutions  of  lead,  copper,  or  iron  salts,  and 
their  odours  are  closely  similar  ;  but  they  may  be  readily  dis- 
tinguished if  attention  is  paid  to  the  subjoined  differences: 

Ammonmm  Sulphide. — Alkaline  reaction;  produces  a  violet 
colour  with  a  solution  of  nitro-prusside  of  sodium ;  odour  of  rotten 
eggs  and  ammonia. 

Sulphuretted  Hydrogen. — Neutral  reaction;  no  effect  upon  the 
nitro-prusside;  odour  of  rotten  eggs  alone. 


PART   V 

FOOD   EXAMINATION 

The  following  list  shows  the  results  (expressed  as  a  per- 
centage of  adulterated  samples)  of  analyses  of  samples  taken 
under  the  Sale  of  Food  and  Drugs  Acts,  during  the  year  1912,  in 
England  and  Wales : 


Milk,  10-9  per  cent. 
Wine,  10-6 
Spirits,  g-6      ,, 
Butter,  6-0      ,, 
Confectionery  and  jam, 

5-5  per  cent. 
Beer,  5-5  per  cent. 
Sugar,  5-1 
Coffee,  4-8 


Cocoa,  3-4  per  cent. 
Flour,  2-6 
Cheese,  2-5        ,, 
Mustard,  2.5     ,, 
Margarine,  2-i  ,, 
Pepper,  o-8 
Lard,  0-4  ,, 

Bread,  o-o         ,, 
Tea,  0-0 


CHAPTER  I 

MILK 

The  Composition  of  Cow's  Milk  and  of  Other  Milk. 

Milk  consists  of  water,  proteids,  milk-sugar  {C-y2^22^i-i)  ^^^ 
mineral  salts  (chiefly  phosphates  of  calcium,  magnesium  and 
potassium,  and  chlorides  of  sodium  and  potassium;  very  small 
quantities  of  sulphates  are  present,  and  traces  only  of  carbonates, 
if  any). 

The  fat  is  suspended  as  minute  globules,  and  since  it  forms 
the  lightest  element  in  the  milk  it  tends  to  rise  to  the  surface  in 
the  form  of  "cream,"  the  largest  globules  being  the  first  to 
separate.  The  milk  early  undergoes  a  souring,  followed  b}^  a 
natural  separation  into  a  solid  "  curd  "  and  a  liquid  "  whey." 

225  13 


226  LABORATORY  WORK 

This  change  is  caused  by  the  fermentative  conversion  of  the 
milk-sugar  into  lactic  acid  by  the  agency  of  micro-organisms 
which  gain  access  to  the  milk,  the  chief  of  which  is  known  as 
Bacilkts  acidus  ladicus.  Acetic,  succinic,  and  carbonic  acids  are 
also  produced  in  small  amounts. 

The  "  curd  "  is  fomid  to  consist  of  casein,  albumin,  and  traces 
of  other  kindred  nitrogenous  substances;  the  "whey,"  of  the 
water,  milk-sugar,  and  salts. 

A  still  later  change  is  characterized  by  the  appearance  of  a 
bluish  tint,  which  is  ascribed  to  the  growth  of  another  micro- 
organism, called  Bacillus  syncyamis ;  and  ultimately  the  casein 
decomposes  owing  to  the  access  and  development  of  putrefactive 
bacteria. 

The  average  composition  of  piire  cow's  milk  is  as  follows: 


Water,  87-40. 

Solids,  12 -60,  consisting  of 


Sugar,  475. 
Fat,  3-65. 
Proteids,  3-48. 
,]\Iineral  salts,  072. 


\'ieth's  ratio  of  the  sugar,  proteids  and  ash  in  cow's  milk  is 
13  :  9  :  2. 

The  milk  of  individual  cows,  collected  imder  circumstances 
which  preclude  the  possibility  of  any  sophistication,  has,  how- 
ever, been  found  to  var}-  considerably  in  its  composition. 

There  is  no  parellelism  between  rainfall  and  composition  of 
cow's  milk;  and  from  experiments  undertaken  by  the  Board  of 
Agriculture  it  appears  that  the  excessive  drinking  of  water  by 
cows  has  no  direct  bearing  on  the  composition  of  their  yield. 
The  circumstances  which  mainly  determine  the  variations  are : 
{a)  The  breed  of  the  cow.  Alderneys  give  most  fat,  and 
Longhorns  most  casein. 

{b)  The  time  which  has  elapsed  since  the  last  milking.  The 
longer  the  interval  between  the  milkings  the  poorer  the  quality. 
Richmond  finds  that  evening  samples  generally  show  from  0-3 
to  0-4  per  cent,  more  fat  than  morning  samples. 

(c)  The  stage  of  milking.  That  which  is  first  drawn  ("  fore- 
milk ")  contains  very  little  cream  (under  0-5  per  cent.);  but 
towards  the  end  of  the  milking  the  cream  is  very  high  in  amount ; 
and  the  very  last  quantities  drawn  from  the  udder  ("  the  strip- 
pings  ")  are  almost  pure  cream. 


MILK 


227 


(d)  The  health  of  the  animal. 

{e)  The  age ;  young  cows  secreting  milk  of  a  poorer  quality. 

(/)  The  time  of  year.  The  lowest  fat  occurs  in  April,  May 
and  June,  and  the  highest  in  October;  and  during  July  and 
August  the  solids-non-fat  are  below  the  average. 

(g)  The  period  which  has  elapsed  since  last  calving,  affecting 
the  presence  or  absence  of  colostrum  and  the  richness  of  the  milk. 
The  total  solids  (especially  the  fat)  increase  with  the  advance  of 
the  lactation  period. 

(h)  The  food  taken ;  beet  and  carrots  throw  up  the  sugar. 

Where  the  amount  of  fat  is  very  high  the  solids-non-fat  are 
frequently  below  the  average  in  pure  milk,  the  deficiency  being 
due  to  deficiency  in  milk-sugar  and  not  to  proteids  or  ash;  and 
a  cow  yielding  a  high  figure  of  fat  in  the  afternoon  may  give 
below  the  average  in  the  morning. 

It  is  very  rare,  however,  that  in  dairy  samples  containing  the 
mixed  milk  of  several  cows  the  non-fatty  solids  fall  below  8-5  per 
cent.,  or  the  fat  below  3  per  cent. 

The  following  table  (after  D.  Richmond)  shows  a  comparison 
between  the  milk  of  various  animals : 


Casein, 

Water. 

Albumin, 
etc. 

Fat. 

Sugar. 

Salts. 

Human  .  . 

87-80 

2-20 

3-30 

6-40 

0-30 

Cow         

87-20 

3-57 

3-76 

475 

0-72 

Ewe 

79-46 

6-68 

8-63 

4-28 

0-97 

Goat 

86-04 

4-35 

4-63 

4-22 

0-76 

Mare        

89-80 

1-84 

I-17 

6-89 

0-30 

Ass 

90-12 

1-66 

1-26 

6-50 

0-46 

It  will  be  seen  from  this  table  that  the  proteid  material  varies 
from  2-20  in  human  milk  to  6-68  in  the  ewe;  that  the  fat  is  lowest 
in  the  mare's  milk  (1-17),  and  highest  in  the  ewe's  (8-63);  that' 
sugar  ranges  from  4-22  in  the  goat  to  6-89  in  the  mare;  and  that 
the  water  is  least  in  amount  in  the  ewe's  milk  (79-46),  and  greatest 
in  that  of  the  ass  (90-12). 

Thus,  adopting  the  cow's  milk  as  a  standard  for  comparison, 
human  milk  (though  var5nng  greatly  with  the  period  of  lactation, 
etc.)  shows  an  increased  quantity  of  sugar  and  a  slightly  in- 
creased quantity  of  water;  but  all  solid  constituents,  with  the 
exception  of  sugar,  are  materially  less,  the  total  proteids  amount- 


228  LABORATORY   WORK 

ing  to  less  than  one-half.  Marc's  milk  is  also  richer  in  sugar 
and  water;  but  the  fat,  casein,  albumin  and  ash  are  considerably 
less.  Goat's  milk  is  richer  in  the  solid  constituents  except  sugar, 
and  therefore  contains  a  less  percentage  of  water.  Ewe's  milk 
is  characterized  by  the  very  high  amount  of  fat,  casein  and 
albumin;  the  ash  is  higher  than  in  cow's  milk,  but  the  sugar 
and  water  are  less. 

Citric  acid  is  a  normal  constituent,  in  minute  quantity,  of 
cow's  milk  and  of  human  milk. 

The  Milk  of  Diseased  Cows. 

Although  the  milk  secretion  is  in  abeyance  during  some  diseases, 
it  is  not  so  in  all,  nor  is  it  so  in  all  cases  of  the  same  disease.  In 
a  few  conditions  the  milk  presents  somewhat  definite  chemical 
and  microscopical  characters;  to  the  naked  eye  it  may  be  all 
that  is  desired. 

It  is  in  cattle  plague  and  foot  and  mouth  disease  that  the 
changes  are  most  marked. 

1)1  cattle  plague  the  sugar  is  markedly  diminished;  the  fat  is 
increased,  together  with — to  a  less  extent — the  casein  and  salts 
(Gamgee) .    Blood  and  pus  are  also  commonly  detected  in  the  milk. 

In  foot  and  motUh  disease  the  milk  commonly  contains  pus, 
blood,  or  mucus  {i.e.,  in  those  cases  where  there  is  ulceration  of 
the  teats  or  abscesses  in  the  udder) ;  and,  as  in  cattle  plague, 
the  milk  corpuscles  are  seen  under  the  microscope  to  display  a 
tendency  to  aggregate  into  grape-like  clusters.  M'hen  the 
disease  is  advanced,  bodies  resembling  pus  cells  (though  a  little 
larger),  and  large  yellow  granular  bodies,  together  with  pus  and 
blood  cells,  are  also  present.  In  this  disease  the  results  of 
chemical  analyses  vary  so  considerably  as  to  be  of  no  value 
for  diagnostic  purposes;  but  the  milk  separates  remarkably 
quickly  on  the  application  of  a  gentle  heat  into  curds  and  a 
pale  blue  whey;  and  this  feature  alone  is  considered  as  almost 
diagnostic  by  some  Continental  observers. 

In  tuberculosis  the  milk  is  not  at  first  appreciably  affected, 
but  the  fat,  lactose,  and  casein  diminish  toward  the  later  stages 
of  the  disease. 

In  garget  the  milk  from  the  inflamed  quarters  of  the  udder  is 
often  thin  and  poor  in  solid  constituents,  and  blood  and  pus  may 
be  present. 


CHAPTER  II 

THE  ANALYSIS  OF  MILK 

The  Physical  Characters: 

1.  Consistence. — The  milk  should  be  quite  opaque  when  placed 
in  a  narrow  glass  tube;  otherwise  it  has  probably  been  watered, 
and  haf^  a  bluish  tint. 

Sometimes  it  is  thick  and  viscid  ("  ropy  "),  and  on  pouring  has 
an  appearance  somewhat  akin  to  mucus.  Such  milk  has  the 
property  of  imparting,  when  added  in  small  quantities,  its  own 
peculiar  quaUty  to  large  bulks  of  good  milk.  This  condition  may 
be  due  to  inflammation  of  the  udder  or  to  the  growth  of  certain 
micro-organisms,  whereby  a  mucinous  substance  results  from 
changes  in  the  milk-sugar  and  casein.  It  is  usually  accompanied 
by  considerable  acidification. 

"  Colostrum  "  (the  milk  yielded  during  the  first  few  days  after 
the  birth  of  the  calf)  coagulates  on  heating,  owing  to  the  larger 
quantity  of  albumin  it  contains;  it  is  also  more  yellow  than 
ordinary  milk,  shows  flocculi,  and  has  a  slightly  insipid  saline 
taste.  Some  milks  coagulate  shortly  after  being  drawn;  these 
are,  of  course,  very  acid,  and  are  generally  yielded  by  cows  in 
febrile  conditions  while  suffering  from  inflammation  of  the 
udder. 

2.  Colour. — ^The  colouring  matter  of  milk  (lactochrome)  is  in 
association  with  the  fat  globules  and  to  a  slight  extent  with  the 
casein ;  and  as  soon  as  the  fat  is  separated  in  the  form  of  cream, 
the  original  colour  largely  disappears.  A  good  milk  should 
be  white  with  the  faintest  possible  suspicion  of  yellow,  although 
such  food  as  buttercups,  carrots,  mangel-wurzel,  etc.,  tend  to 
increase  the  yellow  colour.  A  marked  yellow  may  also  occur 
naturally  in  milk  containing  considerable  quantities  of  colostrum 
corpuscles,  where  the  animal  is  jaundiced,  or  where  there  are 
certain  congestive  conditions  of  the  udder.     The  colour  is  also 

229 


230  LABORATORY    WORK 

artificialh-  furnished  by  dairymen  b}^  means  of  the  addition  of 
colouring  agents. 

Rarely,  the  freshly  drawn  milk  is  of  a  faint  blue  hue,  or  even 
green,  or  reddish.  The  cause  of  these  colorations  has  been 
ascribed  to  the  food  consumed  and  also  to  micro-organisms. 
Such  milks  have  been  known  to  cause  severe  gastro-intestinal 
irritation;  and  more  especially  is  this  the  case  with  "blue" 
milk.  When  these  colours  form  slowly  after  the  milk  has  been 
drawn,  it  seems  probable  that  they  are  due  to  micro-organisms 
(such  as  B.  cyanogemts). 

A  pinkish  hue  is  sometimes  created  by  the  presence  of  blood, 
but  generally  the  blood  tends  to  deposit. 

3.  Taste  and  Odotir. — Milk  has  the  power  of  absorbing  any 
odorous  gases  with  which  it  comes  in  contact,  and  of  acquiring 
and  retaining  distinct  flavours  from  the  food  consumed  by  the 
animal  secreting  it;  thus  cows  which  have  been  feeding  upon 
turnips,  garlic,  fennel,  damaged  ensilage,  distiller}'-  grain,  etc., 
yield  a  milk  which  tastes  of  these  articles ;  and  when  bitter  medi- 
cines have  been  administered,  or  chestnut  or  vine  leaves  have 
been  eaten,  or  when  the  cow  suffers  from  some  forms  of  liver 
disease,  a  bitter  flavour  is  imparted  to  the  milk.  A  bitter  flavour 
may  also  be  produced  by  certain  micro-organisms. 

4.  Reaction.— This  may  be  neutral  or  alkaline  when  freshly 
drawn  from  the  udder,  but  the  milk  is  commonly  amphoteric  in 
reaction,  turning  red  litmus-paper  blue  and  blue  litmus-paper 
red.  This  amphoteric  reaction  with  litmus  results  from  the 
presence  of  two  salts  with  opposite  reactions.  The  acid  reaction 
is  due  to  the  primary  sodium  phosphate  (NaH2P04),  and  the 
alkaline  to  the  secondary  phosphate  (Na2HP04).  Milk  is 
generally  faintly  acid  by  the  time  it  comes  to  be  analyzed;  if 
markedly  acid,  lactic  acid  fermentation  has  well  set  in;  and  if 
markedly  alkaline,  some  alkaline  salt  (such  as  sodium  bicar- 
bonate) may  have  been  added. 

The  acidity  may  be  calculated  by  running  into  50  c.c.  of  the 
sample  ,F^  sodium  hydrate  (phenolphthalein  being  used  as  the 
indicator),  each  c.c.  representing  "  i  degree  "  of  acidity;  this 
multiplied  by  0-009  gives  the  percentage  expressed  as  lactic 
acid  (Richmond).  (A  degree  of  acidity  represents  i  c.c.  of  N. 
acid  to  the  litre,  or  i  c.c.  of  -^  acid  to  100  c.c.)  Milk  as  sold  to  the 
consumer  should  not  curdle  when  shaken  up  in  a  test-tube  with 
an  equal  bulk  of  spirit  containing  70  per  cent,  of  alcohol  by 


THE    ANALYSIS    OF   MILK  23I 

volume.  On  inclining  the  test-tube  and  bringing  it  back  to  the 
vertical  position  flakes  or  films  adhere  to  the  sides  if  the  acidity 
is  above  8  degrees. 

5.  Sediment.— Any  foreign  suspended  matter  is  generally 
readily  seen  on  the  white  background  which  the  fluid  itself  pre- 
sents; and  any  such  matter  may  be  detected  at  the  bottom 
of  the  cream  tube  after  the  milk  has  stood  in  this  for  several 
hours.  Dirt  (cow-dung,  dust,  grit,  hairs,  textile  fibres,  pus, 
blood,  epithelium,  etc.)  will  deposit  on  standing,  especially  if 
the  milk  is  well  diluted  with  water. 

The  dirt  in  mflk  may  be  estimated  by  taking  100  c.c.  of  the 
sample,  centrifugaHzing  this,  and  decanting  the  fluid  portion. 
The  sediment  is  then  shaken  with  15  c.c.  of  10  per  cent,  ammonia, 
the  mixture  being  diluted  after  the  lapse  of  one  hour  with  water 
and  again  centrifugalized.  The  opalescent  liquid  is  then  de- 
canted, the  sediment  washed  with  water  into  a  weighed  platinum 
crucible,  and  further  washed  successively  with  alcohol  and  ether. 
The  crucible  and  its  contents  are  then  dried  at  100°  C  until 
constant  in  weight  (Fendler  and  Kuhn). 

Useful  comparative  data  as  to  dirt  may  be  obtained  by  filtering 
samples  through  cotton  discs,  when  the  discs  (which  should  be 
supported  on  wire  gauze)  are  i  inch  in  diameter  and  a  pint  of 
each  sample  is  so  filtered.  If  a  vacuum  pump  is  employed  the 
milk  is  quickly  drawn  through  the  disc. 

Eau  de  javelle  completely  dissolves  such  cellular  elements  as 
leucocytes,  leaving  dirt  which  has  gained  access  since  the  milk 
left  the  udder,  so  that  it  may  be  separately  collected.  To  make 
this  preparation,  20  grammes  of  good  bleaching  powder  are 
rubbed  up  in  a  mortar  with  lOO  c.c.  of  water,  and  the  emulsion 
mixed  with  a  solution  of  20  grammes  of  anhydrous  potassium 
carbonate  dissolved  in  100  c.c.  of  water.  After  thorough  mixing, 
the  gruel-like  mass  is  allowed  to  stand  for  an  hour,  and  then 
filtered  under  pressure.  The  clear  yellowish  liquid  keeps  well 
in  the  dark,  but  prior  to  use  it  should,  if  necessary,  be  again 
filtered. 

A.  W.  F.  Lowe  has  suggested  a  test  for  the  presence  of  bile- 
salts  in  order  to  prove  that  the  dirt  contains  dung.  A  little 
grape-sugar  is  dissolved  in  a  watch-glass  containing  the  sediment, 
the  liquid  is  then  removed  as  closely  as  possible  by  decantation, 
the  sediment  is  dried  at  100°  C,  allowed  to  cool,  and  a  drop  of 
pure  sulphuric  acid  is  run  over  the  particles,  when  a  fine  cherry-red 


232 


LABORATORY   WORK 


crimson  colour  appears  in  the  presence  of  bile-salts.  The  colour 
develops  around  the  particles,  and  it  is  well  to  employ  a  magnify- 
ing glass  for  their  examination. 

"  Incows  clinically  tuberculous  the  faeces  contain  large  numbers 
of  living  tubercle  bacilli "  (Third  Interim  Report  of  the  Royal 
Commission,  appointed  in  1901,  on  Human  and  Animal  Tuber- 
culosis), and  this  circumstance  is  probably  responsible  for  the 
bulk  of  the  infection  of  milk  by  this  germ. 

The  milk  must  be  fresh  at  the  time  of  analysis,  as  after  lactic 
acid  fermentation  of  the  milk-sugar  has  set  in  there  is  a  slight 
loss  in  the  non-fatty  solid  matter. 

One  or  two  drops  of  formalin  will  keep  a  sample  fresh  for 
several  days. 


FIG.    34. THE    CREAM    TUBE. 

The  sample  should  in  every  case  be  thoroughly  mixed  before 
any  part  is  removed  for  analysis. 

The  Cream. — Some  of  the  milk  is  poured  into  a  "  cream  tube." 
This  is  a  glass  cylinder,  the  upper  part  of  which  bears  markings 
that  show  the  proportion  which  the  cream  on  separation  forms 
to  the  total  volume  of  the  milk. 

The  milk  is  made  to  stand  exactly  up  to  the  level  of  the  zero  of 
the  scale  (due  allowance  being  made  for  capillarity),  and  it  is 
then  set  aside  for  twenty-four  hours.  Supposing  the  cream  is 
found  to  reach  down  to  10  on  the  scale,  then  it  is  10  per  cent. ; 
and  so  the  volume  of  cream  is  read  off  against  the  graduated 
scale. 

Generally  the  cream  will  have  separated  in  twelve  hours,  but 
the  separation  is  not  complete  in  all  samples  until  twenty-four 
hours;  if  the  time  is  protracted  beyond  twenty- four  hours,  partial 
drying  ensues,  and  the  resulting  contraction  will  eventually  leave 


THE   ANALYSIS    OF   MILK  233 

a  space  between  the  lower  surface  of  the  cream  and  the  upper 
surface  of  the  milk.  Good  milk  throws  about  lo  per  cent,  of 
cream;  but  the  milk  of  an  Aldemey  cow  may  yield  between  30 
and  40  per  cent. 

Fresh  cream  contains  a  very  variable  proportion  of  fat.  Gener- 
ally the  amount  falls  within  40  and  50  per  cent. ;  but  there  may  be 
25  per  cent,  or  less  when  the  cream  is  considerably  diluted  with 
milk. 

Clotted  cream  generally  contains  from  45  to  60  per  cent,  of  fat. 

Before  the  specific  gravity  is  taken,  any  frothing  (from  shaking 
or  pouring  into  the  glass  cylinder)  must  first  be  allowed  to  pass  off. 

Westphal's  balance  is  a  rapid  and  a  more  exact  method  of 
obtaining  the  specific  gravity  of  milk  than  a  hydrometer  (lacto- 
meter) {vide  p.  8). 

The  specific  gravity  of  distilled  water  at  15-5°  C.  being  taken 
as  1,000,  that  of  pure  milk  at  the  same  temperature  is  commonly 
about  1,032.  The  fat  is  so  much  lighter  than  the  remainder  of 
the  milk  that  with  its  removal  the  specific  gravity  rises  even 
higher  still.  A  specific  gravity  much  above  1,032  will  therefore 
create  suspicion  as  to  the  removal  of  the  lighter  element  (cream) 
from  the  milk.  The  addition  of  water  will  lower  the  specific 
gravity  again,  for  it  is  obvious  that  the  specific  gravity  of  water 
being  1,000,  the  more  of  this  is  added  the  nearer  will  the  specific 
gravity  of  the  mixture  of  milk  and  water  be  reduced  to  1,000. 
An  abundance  of  cream  will  also  account  for  a  low  specific  gravity 
of  milk,  so  that  a  low  specific  gravity  may  mean  either  abundance 
of  cream  or  the  addition  of  water. 

It  follows,  then,  that  the  specific  gravity  and  cream  tests  con- 
sidered together  afford  a  valuable  clue  as  to  the  nature  of  the 
sample. 

The  total  solids  are  estimated  in  the  following  manner: 

Pipette  5  c.c.  of  milk  into  a  weighed  platinum  dish.  Curdle 
this  by  adding  to  it  a  few  drops  of  a  mixture  of  one  part  acetic 
acid  to  nine  parts  of  methylated  spirit;  this  will  prevent  any 
skin  forming  on  the  surface,  and  will  greatly  hasten  the  drying. 
Dry  first  on  the  water-bath,  then  for  two  hours  inside  the  water- 
oven  at  a  temperature  not  exceeding  105°  C.  Let  cool  and  w^eigh. 
From  this  total  weight  subtract  the  weight  of  the  dish.  Multiply 
the  remainder  by  20  to  bring  it  to  100  parts.  Now  convert  the 
100  c.c.  of  milk  to  weight,  by  deducing  this  from  the  specific 
gravit}/,  and  then  calculate  the  percentage  of  solids  by  weight. 


234  LABORATORY   WORK 

Example. — Solids  +  dish  weighed  12-903  grammes. 
Deduct  weight  of  dish  12-203 

0-700  gramme  in  5  c.c. 
Multiply  by  20  =  14-00  grammes  of  solids  in  100  c.c.  of  milk. 
Now,  if  the  specific  gravity  of  the  milk  is  1,030,  the  weight  of 
milk  as  compared  with  that  of  distilled  water  is  as  1,030  is  to 
i.ooo;  and  as  100  c.c.  of  water  weigh  100  grammes,  100  c.c.  of 
tlie  milk  will  weigh  103-0  grammes.  And  14-0  grammes  of  solids 
in  103-0  grammes  of  milk  =  13-59  P^r  cent. 

Richmond's  formula  for  total  solids  is:  0-25  G+i-2  F  +  0-14; 
where  F==fat  and  G  =  the  last  two  figures  of  specific  gravity 
and  any  decimal.  The  result  maybe  rapidly  obtained  by  means 
of  Richmond's  Slide  Rule. 

Mineral  Ash. — Ignite  the  total  solid  residue  until  all  dark 
specks,  etc.,  have  disappeared,  and  nothing  but  a  perfectly  clean 
whitish  ash  remains.  The  ignition  must  be  effected  slowly  and 
at  as  low  a  temperature  as  possible;  Bell  recommends  that  an 
Argand  burner  should  be  used  in  preference  to  a  Bunsen,  on  this 
account. 

The  ash  is  then  weighed,  and  its  percentage  amount  by  weight 
ascertained  in  a  similar  manner  to  the  total  solids.  Too  large  a 
proportion  of  ash  (that  is,  above  0-75  per  cent.)  points  to  the 
addition  of  mineral  matter.  A  milk  may  have,  on  the  other 
hand,  a  paucity  of  ash,  due  to  the  copious  admixture  of  water. 

Effervescence  on  the  addition  of  hydrochloric  acid  denotes 
adulteration  by  a  carbonate,  which  will  generally  be  sodium  car- 
bonate. The  ash  of  a  pure  milk  does  not  effervesce  when  hydro- 
chloric acid  is  added  to  it. 

The  Fat. — There  are  many  methods  in  use  at  the  present  day 
for  the  extraction  and  estimation  of  fat.  The  student  is  recom- 
mended to  employ  Schmidt's  process,  and,  where  necessary  or 
desirable,  to  corroborate  results  by  Adam's  process. 

The  Werner-Schmidt  Process. 

This  process  has  become  a  favourite  one,  for  by  it  a  very 
accurate  estimation  of  the  fat  can  be  made  in  a  short  space  of 
time. 

The  process  is  as  follows : 

I.  A  specially  graduated  tube,  as  shown  in  Fig.  35,  is  employed 
to  receive  10  c.c.  of  milk,  to  which  10  c.c.  of  strong  hydrochloric 


THE   ANALYSIS    OF    MILK 


235 


acid  is  added;  the  milk  and  acid  thus  standing  to  the  mark  ot 
20  c.c.  on  the  tube. 

2.  The  mixture  is  boiled,  with  frequent  shaking,  until  it  turns 
a  brown  colour  (from  the  conversion  of  milk-sugar  into  maltose 
and  caramel) . 

3.  Let  stand  for  about  three  minutes,  then  cool  by  immersion 
in  a  stream  of  water. 

4.  Fill  up  to  the  50  c.c.  mark  with  ether;  cork  the  tube  and 
invert  it  three  times;  then  set  aside  for  fifteen  minutes,  when  the 
ether  will  have  separated. 

5.  Accurately  pipette  off  20  c.c.  of  the  clear  supernatant 
ethereal  solution  of  fat  into  a  weighed  flask,  and  evaporate  off 


FIG.    35. — stokes'    tube    FOR    THE    WERNER-SCHMIDT    PROCESS. 

the  ether,  until  the  last  small  bubble  disappears.  A  naked  flame 
must  not  be  brought  near  to  the  ether,  so  it  becomes  necessary 
to  drive  off  the  ether  by  placing  the  flask  in  hot  water.  The 
flask  can  be  attached  to  a  condenser  and  the  ether  recovered  for 
subsequent  use. 

6.  Dry  in  air-bath  at  100°  C,  and  weigh  the  residual  fat. 

7.  Next  notice  how  many  c.c.  of  ethereal  solution  remain  in 
the  tube;  then  from  the  fat  estimated  in  the  20  c.c.  calculate 
the  amount  of  fat  in  the  whole  of  the  ether. 

Example. — Ten  c.c.  of  milk,  with  a  S.G.  of  1,031,  gives  in  20  c.c. 
ethereal  solution  0-277  gramme  of  fat. 

In  the  tube  there  remained  6-5  c.c.  of  ethereal  solution,  making 

26''^  X  0'27'7 

a  total  of  26-5  c.c.    .-• '^^-^  =0-367  gramme  of  fat  in  the 

10  c.c.  of  milk,  or  3-67  grammes  in  100  c.c.  But  100  c.c.  of  milk 
with  a  specific  gravity  of  1,031  weighs  103-1  grammes.     Therefore 


236  LABORATORY   WORK 

there  are  3-67  grammes  of  fat  in  103-1  of  milk,  or  3-559  per 
cent. 

Notes  upon  the  Process. — There  floats  between  the  brown 
mixture'  of  HCl  and  milk  and  the  ethereal  solution,  a  fluffy 
stratum  of  casein.  Three-fourths  of  this  stratum  should  be 
taken  as  ether  in  reading  off  the  quantity  of  the  latter. 

The  acid  and  milk  should  not  be  boiled  together  for  more  than 
two  minutes,  or  the  ether  takes  up  a  caramel-like  substance. 

The  whole  process  does  not  take  more  than  forty  minutes ;  and 
it  is  well  adapted  for  use  where  the  milk  has  decomposed. 

The  boiling  with  HCl  converts  the  albumin  into  soluble  acid 
albumin,  and  the  fat  is  then  fully  exposed  to  the  action  of  the 
ether. 

Adam's  Process. 

This  process,  by  which  an  extremely  thin  layer  of  milk  is 
spread  over  absorbent  paper  and  the  fat  then  extracted  by  ether, 
gives  very  exact  results. 

1.  Shake  the  sample,  and  pipette  5  c.c.  into  a  small  beaker 
about  2  inches  deep  and  1  i  inches  wide,  then  weigh. 

2.  Soak  up  as  much  of  the  milk  as  possible — and  in  every  case 
almost  the  entire  5  c.c- — by  a  coil  of  white  demi-blotting-paper 
keeping  the  beaker  covered  during  the  absorption. 

It  is,  of  course,  imperative  that  the  paper  should  be  freed  from 
fat  prior  to  its  employment.  This  may  be  done  by  extracting 
it  with  acid  alcohol  (alcohol  containing  10  per  cent,  of  acetic 
acid)  for  at  least  three  hours,  and  then  thoroughly  drying;  or 
the  specially  prepared  slips  of  fat-free  paper  made  by  Messrs. 
Schleicher  and  Schiill,  of  Diiren,  may  be  used.  A  hehcal  coil  is 
prepared  by  rolling  a  strip  of  the  paper  upon  a  glass  rod  of  the 
size  of  a  cedar  pencil,  care  being  taken  not  to  tear  the  paper ;  and 
the  coil  may  be  held  together  with  platinum  wire. 

3.  Remove  the  coil  by  its  upper  part,  and  place  it  dry  end 
downwards  upon  a  slip  of  glass,  and  then  re-weigh  the  beaker 
with  the  trace  of  milk  left  behind  in  it.  The  difference  in  weight 
from  the  previous  weighing  represents  the  weight  of  milk  soaked 
up  by  the  coil. 

4.  Dry  the  coil  in  the  water-oven  for  two  hours,  and  then 
extract  the  fat  by  anhydrous  ether  in  a  Soxhlet,  twelve  syphonings 
at  least  being  necessary  {vide  p.  9). 

5.  Receive  the  fat  and  ether  in  a  small   light  flask;  drive  off 


THE   ANALYSIS   OF   MILK  237 

the  ether;  dry  to  constancy  in  awater-oven  at  about  105°^.  the 
flask  being  laid  in  a  horizontal  position ;  let  cool,  and  weigh  the  fat. 

Notes  upon  the  Process.-^By  the  addition  of  ammonia  sour 
milk  is  as  easily  taken  up  as  fresh. 

A  good  anhydrous  ether  may  be  prepared  by  placing  the  com- 
mercial article  of  S.G.  0720  for  three  weeks  over  qmckhme,  and 

then  distilhng. 

To  obviate  the  two  weighings,  some  analysts  apply  the  process 

as  follows :  , .  1  j,   1  • 

Suspend  a  strip  of  ^at-free  filter-paper  over  a  lighted  gas-ring 
at  such  a  distance  above  it  as  would  not  be  too  hot  for  the  hand 
to  bear  Distribute  over  this  from  a  pipette  5  ex.  of  miik 
When  dry,  roll  up  the  coil  and  place  it  in  a  Soxhlet's  fat-extractor 
with  some  anhydrous  ether.  Cause  the  ether  to  syphon  over  at 
least  twelve  times  into  a  weighed  flask.  Finally,  drive  off  the 
ether  and  weigh.     Calculate  as  described  above. 

For  rapid  "  samphng  "  purposes  the  foUowing  process  is  useful, 
and  the  results  are  closely  approximate  to  those  obtamed  by 
other  processes : 

M.  Gerber's  Modification  ol  the  Leffmann-Beam  Process. 
A  smafl  test-bottle  is  employed  with  a  thin,  graduated  neck; 
into  this  is  placed  10  c.c.   of  sulphuric  acid  (specific  gravity 
1-82^  at  15.5°  C),  I  c.c.  of  amyl  alcohol  (specific  gravity,  O'Sib 
at  IV5°  C),  and  11  c.c.  of  the  milk  sample.     The  purity  and 
strength  of  the  acid  are  very  important  for  securing  accurate 
results     The  alcohol  and  milk  are  allowed  to  flow  down  the 
side  of  the  bottle,  so  that  the  three  hquids  form  distmct  layers; 
the  bottle  is  then  firmly  corked  and  smartly  shaken  until  the 
curd  is  dissolved.     It  is  then  held  upside  down  to  aUow  the 
acid  to  run  down  the  neck,  and  this  may  be  repeated  two  or 
three  times  to  ensure  that  all  the  ingredients  are  well  mixed. 
The  bottle  is  then  placed  in  a  centrifuge,  which  is  spun  for  three 
minutes  (at  about  1,000  revolutions  per  minute);  or  for  nine 
minutes  in  the  case  of  separated  milk.     If  only  one  sample  is 
being  tested,   another  bottle  should    be  filled  with  milk  and 
placed  opposite  the  sample  bottle,  in  order  to  balance  it  m  the 
centrifuge.     Upon  removal  the  test-bottle  is  placed  neck  down- 
wards into  water  for  two  or  three  minutes  at  a  temperature  of  60 
to  70°  C.  to  keep  the  fat  hquid.     The  percentage  weight  of  fat 
may  now  be  read  off  in  the  graduated  neck  of  the  bottle,  each  of 


23vS  LABORATORY  WORK 

the  finer  divisions  on  which  indicate  o-i  per  cent,  bj^  weight  of 
fat.  In  making  this  reading  the  bottle  should  be  held  vertically, 
and  by  slightly  moving  the  cork  at  the  bottom  of  the  bottle  either 
upward  or  downward,  the  lower  level  of  the  fat  column  in  the 
graduated  neck  may  be  made  to  correspond  to  one  of  the  longer 
markings  which  indicate  whole  percentages  of  fat,  and  from  this 
base  line  the  percentage  of  fat  can  be  easily  and  rapidly  read  off. 


FIG.  36. — CENTRIFUGAL  MACHINE,  FITTED  WITH  TWO  GEARS,  THE  LOW 
GEAR  WORKING  UP  TO  3,000  REVOLUTIONS  PER  MINUTE,  AND  THE 
HIGH    GEAR   UP    TO    10,000. 

Hehner  and  Richmond  have  devised  a  formula  by  means  of 
which  the  fat  in  ordinary  milk  samples  may  be  estimated: 
F=  0-859  T-0-2I86  G;  where  F=fat,  T=  total  solids,  and 
G=the  last  two  units  of  the  S.G.  together  with  any  decimal 
{i.e.,  if  S.G.  =  1029-5,  G=29-5). 

The  solids-not-fat  may  be  calculated  by  subtracting  the  fat 
from  the  total  solids. 

The  Analysis  of  Sour  Milk. — ^Thorpe  has  sliown  that  tlie  l^utter- 
fat  suffers  little,  if  any,  alteration  during  the  souring  of  milk,  but 
that  the  non-fatty  solids  are  more  or  less  affected  by  fermentative 


THE   ANALYSIS    OF    MILK  239 

changes.  The  principal  constituent  which  suffers  change  is 
lactose,  from  a  portion  of  which  lactic  acid  forms  at  an  early 
stage.  As  a  rule  less  than  half  of  the  lactose  (which  averages 
475  per  cent,  in  cow's  milk)  is  thus  transformed. 

Concurrently  with  the  formation  of  lactic  acid,  there  are  pro- 
duced products  which  are  either  gaseous  at  ordinary  tempera- 
tures or  are  volatihzed  during  the  operation  of  determining  the 
non-fatty  contents  of  the  sour  milk.  The  aggregate  weight  of 
these  substances  (acetic  and  butyric  acids,  ethyl  alcohol,  carbonic 
acid,  and  traces  of  ammonia)  is  not  very  large,  but  it  is  sufficient 
to  affect  any  estimation  of  the  degree  of  sophistication  to  which 
the  milk  may  have  been  subjected. 

The  total  loss  of  solid  matter  from  all  causes  ranges,  as  a  rule, 
from  only  o-2  to  0-5  per  cent,  by  weight  of  the  milk,  and  nearly 
the  whole  of  this  is  accounted  for  by  the  transformation  of  lactose 
into  alcohol  and  volatile  acid,  the  changes  in  the  weight  of  pro- 
teid  material  being  relatively  insignificant. 

In  the  analysis  of  a  sample  of  sour  milk  it  is  therefore  recom- 
mended that  the  milk  be  thoroughly  mixed  with  a  wire  whisk ;  the 
lactic  acid  in  the  weighed  quantity  is  then  neutralized  with  -^ 
solution  of  strontia  (using  phenolphthalein  as  indicator),  and 
from  the  total  solid  residue  of  the  milk  the  weight  of  strontia 
added  is  deducted  (each  c.c.  of  y^  strontia=  0-00428  gramme). 

As  regards  the  alcohol,  100  grammes  of  the  milk  are  distilled, 
and  the  distillate  redistilled  after  being  neutralized  with  ^ 
caustic  soda  solution,  litmus-paper  being  used  as  the  indicator. 
The  specific  gravity  of  the  distillate,  made  up  to  the  original 
bulk,  is  determined  in  a  50-gramme  pycnometer,  and  the 
quantity  of  alcohol  corresponding  to  this  specific  gravity  is 
deduced  from  a  table.  The  percentage  by  weight  of  alcohol, 
multiplied  by  f f ,  gives  the  percentage  amount  of  lactose  which 
has  disappeared  in  the  production  of  the  alcohol. 

The  amount  of  volatile  acid  is  ascertained  as  follows : 

Ten  grammes  of  the  milk,  contained  in  a  platinum  capsule,  are 
•neutralized  to  the  extent  of  one-half  the  total  acidity  .(previously 
determined  on  another  portion)  with  |^  caustic  soda,  and  a  little 
phenolphthalein  is  added.  The  mixture  is  then  evaporated  to 
dryness  on  a  water-bath  with  frequent  stirring,  and  after  treat- 
ment with  about  20  c.c.  of  boiling  distilled  water,  so  as  to  break 
up  and  thoroughly  detach  the  milk  solids  from  the  capsule,  a 
further  addition  of  ^  caustic  soda  is  made,  until  the  neutral 


240  LABORATORY   WORK 

point  is  reached.  The  difference  between  the  original  acidity 
of  the  milk  and  that  of  the  evaporated  portion  is  regarded  as 
acetic  acid.  The  production  of  each  molecule  (60  parts)  of  this 
acid  denotes  a  loss  of  i  molecule  of  carbon  dioxide  and  i  of  water 
— that  is,  a  loss  of  62  parts  of  the  original  lactose. 

The  entire  correction,  which  is  always  additive  in  a  properly 
sealed  sample  from  three  to  six  weeks  old,  is  fairly  constant,  and 
generally  ranges  between  o-2  and  0-3  per  cent. 

Microscopical  Examination. — Ten  c.c.  of  milk  should  be  diluted 
with  about  30  c.c.  of  water,  then  centrifugalized  (at  least  1,500 
revolutions  per  minute),  the  supernatant  fluid  decanted,  the  sedi- 
ment washed  with  water  and  placed  on  glass  slides,  and  the 
contents  of  the  slides  examined. 

Normal  milk  under  the  microscope  consists  of  a  collection  of 
round  highly  refractile  oil  globules  of  about  the  same  dimensions, 
with  an  occasional  epithelial  cell ;  from  three  to  eight  days  after 
calving  colostrum  corpuscles  are  also  present  in  larger  or  smaller 


if.. 


V.O-' 


FIG.    37. — MILK    SHOWING    THE    L.\RGE    COLOSTRUM    CORPUSCLES.       (X25O.) 

quantities  (Fig.  S7)-     These  latter  mostly  consist  of  large  yellow 
cells  containing  larger  and  smaller  fat  globules  in  their  interior. 

Where,  however,  the  animal  is  not  in  health,  the  following 
abnormal  constituents  may  also  be  found: 

Cast  of  the  lacteal  tubes,  blood-corpuscles  (which  closely 
resemble  those  of  the  human  subject),  pus  cells  and  leucocytes, 
and  various  micro-organisms  {e.g.,  fungi,  such  as  Oidium  lactis  ; 
moulds,  such  as  penicillium;  and  bacteria).  Blood  may  be 
detected  either  by  the  spectroscope  or  microscope.  When  present 
in  considerable  quantities  blood  tinges  the  milk  and  has  a  tendency 
to  settle  as  a  brown  deposit ;  or  after  warming  the  milk  to  about 
50°  C,  a  high  speed  centrifuge  may  furnish  a  red  deposit  in  the 
milk  tube. 

Cow-dung  shows  vegetable  parenchyma  and  vessels  of  a  dis- 
tinct yellow  tint. 

In  the  deposit  there  may  be  also  detected  yeast  cells,  cotton 
fibres,  hairs,  etc. 
All  milk  samples  contain  a  certain  number  of  cellular  elements, 


THE   ANALYSIS    OF   MILK  24I 

and  in  certain  pathological  conditions  their  number  is  enormously 
increased.  Deductions  of  great  value  can  be  made  from  accurate 
determinations  of  their  number  in  the  milk  of  individual  cows, 
but  for  mixed  milk  samples  the  determination  is  of  much  less 
value.  If  the  diluted  milk  is  centrifugalized,  the  sediment 
spread  evenly  over  a  cover-slip,  dried,  and  stained  by  methylene 
blue,  the  number  of  leucocytes  may  be  enumerated  by  means  of 
the  ordinary  Thoma-Zeiss  blood-counting  apparatus. 

It  has  been  suggested  that  the  number  of  these  cells  should 
not  exceed  500,000  per  c.c,  but  it  is  probable  that  such  a  limit 
would  at  times  lead  to  the  condemnation  of  milk  derived  from 
healthy  sources.  These  cellular  elements  have  been  usually 
regarded  as  leucocytes  or  pus  cells,  and  hence  it  is  that  a  standard 
has  been  suggested  for  the  hygienic  control  of  milk.  There  are 
good  grounds,  however,  for  believing  that  most  of  the  cells  found 
are  young  epithelial  cells  and  not  leucocytes.  Savage  has  classi- 
fied these  cellular  elements  into  polymorphonuclear  cells,  lym- 
phocytes, large  leucocytes,  and  doubtful  cells. 

Owing  to  the  difficulty  of  recognizing  pus  cells  from  other 
cells  that  may  be  present,  it  is  not  easy  to  say  how  frequently  pus 
resulting  from  inflammatory  processes  in  the  udder  gets  into  milk ; 
but  in  a  large  percentage  of  cases  cells  indistinguishable  from  pus 
ceUs  are  present.  Lymphocytes,  which  stain  deeply  and  possess 
nuclei  which  occupy  nearly  the  whole  of  the  cells,  are  not  normal 
constituents  of  milk  except  within  three  weeks  of  parturition; 
but,  like  polymorphonuclear  leucocytes,  they  are  occasionally 
present  for  a  few  days  in  the  milk  of  an  apparently  healthy  cow. 
These  bodies  are  found  associated  with  staphylococci  and  strepto- 
cocci generally  in  diseases  of  the  udder,  and  they  are  to  be  found 
associated  with  tubercle  bacilli  in  tubercular  mastitis.  A  high 
cell  count  accompanied  by  streptococci  apparently  indicates 
some  udder  trouble. 


15 


CHAPTER  III 

THE  SOPHISTICATION  OF  IMILK— MILK  PREPARATIONS-^ 
I^IILK  STANDARDS— BACTERIOLOGICAL  NOTE 

Cow's  milk  should  be  the  normal,  clean,  and  fresh  secretion 
obtained  by  completely  milking  the  udder  of  the  healthy  cow, 
properly  fed  and  kept. 

The  Addition  of  Water. — Whether  milk  is  naturally  poor  or  has 
been  made  so  by  the  addition  of  water,  the  dairyman  who  sells 
it  defrauds  the  purchaser,  for  the  latter  demands  and  pays  for 
pure  milk  of  average  quality. 

It  is  clear  that  the  percentage  amount  of  both  fatty  and  non- 
fatty  solids  will  be  reduced  by  any  addition  of  water;  but  the 
estimation  of  the  amount  of  added  water  is  always  made  from 
the  non-fatty  solids,  because  these  depart  less  from  the  average 
than  is  the  case  with  the  fatty  solids.  The  legal  low  limit  for 
non-fatty  solids  is  one  of  8-5  per  cent. 

Supposing,  then,  a  sample  yields  8  per  cent,  of  non-fatty  sohds. 
Then  if  8-5  per  cent,  of  non-fatty  solids  denotes  100  per  cent,  of 
pure  milk,  8  per  cent,  denotes  only  about  94  per  cent,  of  pure 
milk. 

Therefore  there  is  about  94  per  cent,  of  pitre  milk  in  the 
sample,  and  (100-94=)  6  per  cent,  of  water  has  been 
added. 

It  is  sometimes  maintained  by  the  milk-vendor  that  no  water 
has  been  added  and  that  the  milk  is  naturally  poor  milk.  The 
freezing-point  test  is  said  to  be  of  value  in  settling  this  question, 
for  milk  as  drawn  from  the  cow  freezes  at  -  o-550°C.  whatever 
its  solids-non-fat  content ;  but  the  addition  of  water  alters  the 
freezing-point,  and  a  freezing-point  above  -  o-530°C.  is  said  to  be 
conclusive  evidence  of  watering. 

The  ash  should  in  every  case  be  low  when  the  solids-non-fat 
arc  low,  or  some  mineral  adulterant  has  been  added. 

242 


THE    SOPHISTICATION    OF   MILK  243 

Cream  Abstraction.- — Though  the  milk  from  the  same  cow  may 
vary  at  times,  the  mixed  product  of  many  animals  ("  dairy 
samples  ")  varies  but  little. 

The  legal  low  limit  of  3  per  cent,  of  fat  is  one  which  is  reached 
by  all  genuine  dairy  samples  obtained  from  a  fairly  good  herd 
of  cows,  kept  and  fed  under  average  conditions;  though,  as  Bell 
and  others  have  shown,  the  milk  of  individual  cows  may  some- 
times fall  below  this  limit. 

The  percentage  reduction  of  fat  (by  the  removal  of  cream)  is  an 
easy  calculation  after  an  estimation  of  the  fat  has  been  made. 
Suppose  that  the  fat  has  been  found  to  amount  to  just  2*5  per 
cent.     Then  3  per  cent.   -2-5  per  cent.  =  0-5  per  cent,  of  fat  has 

2'  ^  X  TOO 

been  abstracted  from  the  milk;  or =83*3  per  cent,  of  the 

original  fat  remains  and  (100  -83-3=  )  167  per  cent,  of  the  total 
fat  originally  in  the  milk  has  been  removed.  In  cases  where  the 
fat  is  low  and  the  solids-non-fat  are  high  there  can  be  little 
doubt  that  fat  has  been  abstracted,  and  that  the  low  fat  is 
not  due  to  the  dilution  of.  the  milk  with  water. 

The  "  toning  down  "  of  good  milk  by  the  addition  of  separated 
milk  is  much  practised,  and  large  numbers  of  the  samples  analyzed 
are  found  to  barely  reach  the  low  legal  limit  of  3  per  cent, 
of  fat. 

As  milk  stands,  a  certain  proportion  of  the  fat  quickly  rises  to 
the  upper  layers,  and  a  defence  is  sometimes  set  up  by  the 
dairyman  that  a  poor  sample  was  due  to  the  fact  that  such  top 
milk  had  all  been  sold,  and  the  sample  was  some  of  the  last  of  the 
milk  in  the  can.  This  defence  is,  in  many  cases,  a  wcU-recognized 
subterfuge,  for  it  is  the  duty  of  the  vendor  to  mix  the  milk  and 
to  supply  fair  samples  to  one  and  all  alike.  Failure  to  draw  off 
the  "  strippings  "  no  doubt  often  accounts  for  the  low  figure  of 
fat  in  milk. 

Samples  collected  on  Sunday  mornings  are  generally  amongst 
the  poorest,  for  dishonest  tradesmen  adiilterate  on  these  days 
in  order  to  meet  the  extra  demand,  due  to  the  fact  that  more 
people  take  their  meals  at  home  on  that  day. 

In  addition  to  water,  there  are  other  adulterants  added  to 
milk.  Chalk  and  starch  were  formerly  used,  but  they  are  very 
rarely,  if  ever,  employed  at  the  present  day.  Sodium  carbonate 
is  rarely  used  to  preserve  the  milk  and  to  neutralize  it  when 
sour.     It  may  be  tested  for  (E.  Schmidt)  by  adding  10  c.c.  of 


244  LABORATORY   WORK 

alcohol  to  10  c.c.  of  milk,  followed  b}'  a  few  drops  of  i  per  cent, 
solution  of  rosolic  acid.  Pure  milk  yields  a  brownish-yellow 
colour,  but  if  sodium  carbonate  or  borax  is  present  a  more  or  less 
marked  rose-red  colour  appears. 

Boric  and  salicylic  acids,  borax,  "  formalin,"  benzoates,  fluor- 
ides, peroxide  of  hydrogen,  have  been  used  as  milk  preservatives. 
Either  a  mixture  of  boric  acid  and  borax,  or  "  formalin,"  has 
been  generally  employed.  Such  chemical  preservatives  are  now 
prohibited  in  anj^  form  of  milk  by  the  Public  Health  (Milk  and 
Cream)  Regulations,  igi2. 

Boric  acid  with  borax  is  largely  added  to  milk  during  the 
summer  months,  and  the  amount  generall}'  employed  is 
about  5  grains  to  the  pint.  Experiments  go  to  show  that 
not  less  than  4  grains  of  a  mixture  of  boric  acid  and  borax 
are  necessar}-  to  preserve  a  pint  of  milk  for  twenty-four  hours 
in  warm  weather  (Rideal,  Foulerton).  Salicylic  acid  is  not  so 
frequently  employed,  because  of  its  lesser  solubility  and 
unpleasant  taste. 

"  Formalin  "  is  a  commercial  preparation  containing  about 
38  per  cent,  of  formaldehyde. 

"  Mystin  "  (a  mixture  of  formic  aldeh3?de  and  sodium  nitrite) 
has  occasionally  been  emploj^ed  as  a  preservative. 

Annatto  and  turmeric,  coal-tar  d3'es  and  saffron,  are  j-ellow 
colouring  agents  which  arc  added  to  give  the  milk  a  rich 
yellow  appearance.  Annatto  and  coal-tar  dyes  are  chiefly 
emplo3'ed. 

The  tests  for  the  antiseptic  and  colouring  agents  in  milk  are 
given  in  Chapter  XIII.,  which  treats  of  the  subject  of  Anti- 
septics and  Colouring  Agents  in  Food. 

Cream. — Starch  or  gelatine  is  sometimes  added  to  cream  to 
thicken  it.  Gelatine  may  be  detected  by  adding  to  10  c.c.  of  the 
sample,  20  c.c.  of  cold  water  and  10  c.c.  of  a  solution  of  acid 
nitrate  of  mercury.  The  whole  is  then  well  shaken,  allowed  to 
stand  for  live  minutes,  and  then  filtered.  If  much  gelatine  is 
present,  a  clear  filtrate  cannot  be  obtained.  A  portion  of  the 
filtrate  is  mixed  with  an  equal  quantity  of  a  saturated  aqueous 
solution  of  picric  acid,  when  a  yellow  precipitate  forms  if  gelatine 
is  present  (Stokes).  Starch  is  detected  by  the  bluing  with 
iodine  solution. 

Milk  solids  and  other  fats,  and  lime  in  cane-sugar  sjTup,  have 


THE   SOPHISTICATION   OF   MILK  245 

also  been  added  to  cream.  Sucrate  of  lime  may  be  detected  by 
estimating  the  lime  in  the  ash  of  the  cream  (average  percentage 
of  Ca0=22  per  cent,  of  the  ash).  The  same  preservatives  are 
employed  as  in  the  case  of  milk. 

Under  the  Pubhc  Health  (Milk  and  Cream)  Regulations,  1912, 
no  preservative  may  be  added  to  cream  which  contains  less 
than  35  per  cent,  by  weight  of  milk  fat,  whereas  in  cream  con- 
taining 35  per  cent,  or  more  of  milk  fat  the  only  chemical  pre- 
servatives permitted  are  boric  acid,  borax,  or  a  mixture  of  these, 
and  hydrogen  peroxide;  but  the  addition  of  these  preservatives 
is  subject  to  a  system  of  declaration.  Furthermore,  no  thicken- 
ing substance  may  be  added  to  cream.  In  these  Regulations 
"  thickening  substance  "  means  sucrate  of  hme,  gelatine,  starch 
paste,  or  any  other  substance  which,  when  added  to  cream,  is 
capable  of  increasing  its  thickness.  Neither  cane  nor  beet 
sugar  are  to  be  regarded  as  a  preservative  or  as  a  thickening 
substance. 

Hand-skimmed  milk  is  sometimes  made  to  look  like  good  rich 
milk  by  the  addition  of  condensed  milk.  An  analysis  of  the  ash 
and  non-fatty  sohds  will  detect  the  fraud,  since  these  will  both 
be  in  excess  of  their  general  proportions  (more  especially  the 
sugar),  and  the  amount  of  soluble  albumin  will  be  diminished 
(Faber) . 

Hand-skimmed  milk  is  generally  slightly  acid,  and  the  specific 
gravity  is  above  1032-5.  The  fat  generally  amounts  to  from 
0-5  to  1-5  per  cent. 

The  bulk  of  the  samples  of  "  separated  milk  "  contain  from 
0"2  to  0*3  per  cent,  of  fat. 

Skimmed  and  separated  milk  must  legally  contain  at  least 
8  7  per  cent,  of  solids-non-fat. 

Separated  milk  is  sometimes  "  enriched  " — that  is,  the  butter- 
fat  taken  out  by  the  separator  is  replaced  by  an  emulsion  of 
some  other  fat.  In  such  case  a  separate  analysis  of  the  fat  of 
"  the  cream  "  must  be  made  by  the  Reichert-Wollny  process, 
as  described  in  the  analysis  of  butter. 

Condensed  milk  may  be  unsweetened  or  sweetened  whole  milk 
(unskimmed  or  non-separated)  concentrated  to  about  one-third 
of  its  original  volume,  and  cane-sugar  added;  or  it  may  be  pre- 
pared from  sweetened  skimmed  or  separated  milk. 

The  following  table,  taken  from  Dr.  Coutts's  Report  to  the 


246 


LABORATORY   WORK 


Local  Government  Board  {191 1),  indicates  the  percentage  com- 
position of  the  chief  classes  of  condensed  milk  upon  the  market : 


Full  Crbam. 

Machine  Skimmkd. 

Sweetened. 

Unsweetened. 

Sweetened. 

Lowest. 

Highest. 

Lowest. 

Highest. 

Lowest. 

Highest. 

1 

Total  solids     . . 
Protein     .  . 

Fat 

Lactose    . . 

Ash 

Cane-sugar 

68-1 

7-3 
8-0 

II-6 
1-6 

36-1 

83-6 
II-4 

13-7 
I7-6 

3-4 
44-6 

29-2 
8-0 
8-2 

II'I 
1-6 

Nil 

38-0 
lO'O 

II-9 
i6'0 

2-5 
Nil 

56-9 
7-6 

O'l 

iO'9 

1-6 

30-4 

79-1 
12-3 

6-5* 
17-0 

2-9 
52-6 

In  the  analj'sis  of  condensed  milk  20  grammes  should  be  taken 
and  made  up  to  100  c.c.  with  water  as  a  stock  solution. 

For  Total  Solids. — Evaporate  5  c.c.  of  this  as  in  the  case  of 
milk. 

For  Ash. — Incinerate  the  above.  The  ash  averages  1-9  to 
2  per  cent. 

For  Fat. — Estimate  by  Adam's  process.  The  fat  averages 
about  10  per  cent. 

The  best  method  for  obtaining  a  rapid  and  accurate  estimate 
of  the  fat  in  sweetened  brands  is  the  Gottheb  process  (the  Werner- 
Schmidt  process  being  inapplicable) : 

Into  a  graduated  100  c.c.  tube  put  10  c.c.  of  above  solution; 
add  I  c.c.  of  40  per  cent,  ammonia;  warm  to  30°  C;  shake; 
add  10  c.c.  alcohol  (95  per  cent.),  and  shake.  Add  25  c.c.  ether, 
and  shake;  add  25  c.c.  petrol-ether,  and  shake;  let  settle;  pipette 
off  25  c.c.  of  the  mixed  ether  solution,  evaporate  this  and  weigh. 
Calculate  as  in  the  Schmidt  process.  The  fat  of  sour  milk,  cream, 
cheese,  butter,  etc.,  may  aJl  be  reliably  estimated  by  this  process. 

For  Total  Sugars  (cane  and  milk). — To  10  c.c.  of  stock  solution 
add  40  c.c.  of  methylated  spirit,  add  one  drop  of  acetic  acid, 
shake  (this  will  precipitate  the  curd  and  fat),  filter.  Evaporate 
20  c.c.  of  the  filtrate,  and  weigh  the  residue.  Now  incinerate  this, 
and  subtract  this  ash  from  the  total  sugar  weight.  Multiply 
the  difference  by  22  5,  and  then  by  5,  to  give  percentage  of  mixed 
sugars.  Apparently  one  should  first  multiply  by  25,  but  allow- 
ance has  to  be  made  for  the  volume  occupied  by  the  precipitated 
*  A  partly  skimmed  milk. 


CONDENSED    MILK  247 

curd  and  fat.     Deduct  milk-sugar  (estimated  Ijy  Fehling's  solu- 
tion), and  the  difference  is  cane-sugar. 

The  milk-sugar  (which  averages  13  to  15  per  cent.)  is  deter- 
mined by  titrating  a  5  per  cent,  dilution  of  the  milk  with  Fehling's 
solution  {vide  pp.  340,  341).  The  cane-sugar  may  subsequently 
be  estimated  by  boiling  the  stock  solution  with  citric  acid,  which 
inverts  the  cane-sugar;  the  solution  is  cooled,  neutralized  with 
potassium  hydroxide  solution,  made  up  to  a  known  volume,  and 
titrated  with  Fehling's  solution. 

Many  brands  of  condensed  milk  contain  a  very  laige  amount  of 
sugar,  the  average  being  38  to  40  per  cent. ;  while  others  are  un- 
sweetened. When  opened,  the  latter  have  inferior  keeping  powers. 
For  Proteids. — Perform  Kjeldahl's  process  on  10  c.c.  of  stock, 
and  multiply  the  N  by  6-38.  The  proteid  matter  averages 
9  per  cent. 

The  "  degree  of  condensation  "  may  be  approximately  gauged 
by  dividing  the  percentage  of  solids  by  12 -6,  when  the  condensed 
milk  is  unsweetened;  or  by  dividing  the  percentage  of  fat  by  3-6  in 
other  cases — 12-6  per  cent,  and  3-6  per  cent,  being,  respectively, 
the  average  amounts  of  total  solids  and  fat  in  milk. 

Brands  of  condensed  whole  milk  (not  "  machine  skimmed  ") 
ought  to  contain  at  least  10  per  cent,  of  milk-fat  and  25-5  per 
cent,  of  non-fatty  milk  solids,  of  which  the  ash  should  constitute 
about  2  per  cent. 

Heated  Milk. — Sometimes  it  is  required  to  know  whether  milk 
has  been  steriHzed  or  boiled.  In  such  a  case  3  c.c.  of  milk  may  be 
mixed  with  i  c.c.  of  a  freshly  prepared  10  per  cent,  solution  of 
hydroquinone,  and  about  15  drops  of  hydrogen  peroxide  added. 
If  the  milk  has  not  been  raised  to  a  high  temperature,  an  imme- 
diate rose  colour  forms,  but  otherwise  no  colour  is  produced,  as 
the  reaction  is  destroyed  by  exposure  to  a  high  temperature. 

The  following  changes  result  when  milk  is  boiled:  Carbonic 
acid  gas  is  expelled  and  the  calcium  and  magnesium  salts  are 
therefore  partially  precipitated;  the  greater  part  of  the  phos- 
phates are  also  precipitated.  There  is  a  slight  diminution  in 
the  organic  phosphorus  originally  present ;  a  partial  decomposi- 
tion of  the  proteins.  The  skin  which  forms  on  the  smTace  (solely 
when  the  heating  is  done  in  an  open  vessel)  consists  mainly  of 
lactalbumin.  This  pellicle  has  approximately  the  foUo\nng 
composition:  Fat,  45-5  per  cent.;  lactalbumin  and  casein,  51  per 
cent. ;  mineral  ash,  3-5  per  cent.     The  normal  emulsion  of  the  fat 


248  LABORATORY   WORK 

globules  is  disturbed,  so  that  the  cream  does  not  rise  to  form  a 
layer  on  the  surface,  the  lactose  is  partially  burnt  (carameliza- 
tion),  and  the  milk  therefore  becomes  slightly  brownish  in 
colour.  The  boiling  destroys  the  ferments  in  the  milk  and 
probably  also  the  antiscorbutic  element  of  raw  milk ;  the  natural 
germicidal  power  of  fresh  raw  milk  is  lost,  and  almost  all  the 
bacteria  are  destroj^ed,  those  left  consisting  of  sporing  forms  and 
certain  highlj' resistant  varieties. 

None  of  these  changes  takes  place,  appreciably,  in  "low  tem- 
perature pasteurization  " — namely,  the  heating  of  milk  to  a 
temperature  of  60°  C  for  thirty  minutes — except  the  great 
reduction  in  micro-organisms. 

Milk  Powders. — These  are  now  very  largely  made,  both  from 
whole  milk  and  from  skimmed  milk.  The  powders  are  cream- 
coloured,  with  a  slight  distinctive  odour.  The  fat  in  whole- 
milk  powder  should  amount  to  at  least  25  per  cent.  This  can  be 
determined  by  the  Gottlieb  process  or  by  the  Soxhlet  method. 
Otherwise  the  analysis  follows  on  the  general  lines  described. 

"  Koumiss  "  consists  of  milk  which  has  been  skimmed  of  some 
of  its  cream  and  sugar  added;  it  is  then  partially  fermented  by 
yeast  or  other  ferments,  wherebj^  much  of  the  sugar  is  converted 
into  lactic  and  carbonic  acids. 

Bean  or  Synthetic  Milk. — In  the  preparation  of  this  milk  soya 
beans  are  washed  and  soaked  in  water,  the  outer  integuments 
being  removed.  The  softened  beans  are  then  ground  between 
millstones  and  the  powder  boiled  with  water  and  filtered  through 
fine  sieves.  A  cream-coloured  liquid  results,  closely  resembling 
milk,  but  with  a  distinct  beany  odour  and  taste.  For  use,  sugar 
is  added  to  suit  the  taste  of  the  consumer.  Bean  milk  on  analysis 
contains  about  2-i  per  cent,  of  fat,  37  per  cent,  proteins,  1-4  per 
cent,  carbohydrates  other  than  sugar,  and  0-4  per  cent,  of 
mineral  ash. 

Milk  Standards. 

In  addition  to  the  legal  standards  at  present  in  force,  certain 
other  standards  are  advocated.  Only  a  small  proportion  (one- 
sixth  to  one-eighth)  by  weight  of  the  cow-dung  which  finds  its 
way  into  milk  is  recoverable  (as  dirt)  from  milk  by  centrifugaliza- 
tion;  but  despite  the  difficulties  involved,  certain  standards  for 
dirt  in  milk  have  been  suggested.  Most  authorities  agree  that 
milk  ;ynelding  more  than  i  part  of  recoverable  dirt  per  100,000 


MILK    STANDARDS  249 

is  dirty.  Houston  suggests  that,  as  a  working  standard,  (i)  the 
deposit  from  a  litre  of  milk  obtained  by  sedimentation  in  a 
special  cylindrical  separating  funnel  after  twenty-four  hours 
should  not  exceed  i  part  per  10,000  by  volume;  and  (2)  when 
the  deposit  from  (i)  is  centrifugalized,  it  should  not  exceed  half 
the  above  amount. 

It  has  been  suggested  that,  as  a  general  rule,  the  recover- 
able dirt  should  not  be  allowed  to  exceed  2  parts  per  100,000  by 
weight,  and  some  advocate  a  standard  as  low  as  i  part.  As  a 
rough  household  standard,  |-  pint  of  milk  placed  in  an  ordinary 
tumbler  should  not  throw  a  visible  sediment  in  two  hours.  But 
dirt  may  be  removed  by  trade  filtration,  which  leaves  behind  the 
harmful  bacteria,  and  therefore  the  only  satisfactory  standards 
are  those  based  upon  bacterial  counts. 

Seasonal  standards  of  total  bacterial  counts  are  serviceable. 
In  Chicago,  for  instance,  1,000,000  bacteria  per  c.c.  of  milk  from 
May  I  to  September  30,  and  half  that  amount  for  the  remainder 
of  the  year,  is  the  standard  of  milk  as  it  arrives  in  that  city. 
Savage  prefers  a  standard  of  lactose  fermenters  of  the  coli  type 
of  not  more  than  100  in  winter  and  1,000  in  summer,  and  he 
suggests  that  initial  contamination  may  be  best  judged  from  the 
number  of  Bacillus  enteritidis  sporogenes  (the  spores  of  which 
abound  in  cow-dung),  as  that  organism  shows  relatively  little 
tendency  to  multiply  in  milk. 

Certainly  leucocytes  exceeding  1,000  per  c.c.  along  with  manj- 
streptococci  suggests  the  desirability  of  investigation. 

In  special  (certificated)  milk,  which  is  sold  at  an  enhanced 
price,  it  is  possible  to  impose  such  high  standards  aS' — freedom 
from  B.  Uiberculosis,  a  total  bacterial  count  below  10,000  per  c.c. 
(Class  A)  and  100,000  per  c.c.  (Class  B),  and  delivery  to  the 
consumer  at  a  temperature  of  not  above  10°  C 

A  suggested  standard  for  pasteurized  milk  is  that  the  total 
bacterial  count  should  not  exceed  1,000,000  per  c.c.  prior  to 
pasteurization,  and  50,000  per  c.c.  when  pasteurized  and  delivered 
to  the  consumer. 

Reductase  test  (Schmidt-MuUer)  may  serve  as  a  standard  for 
freshness.  The  test  reagent  is  made  by  adding  5  c.c.  of  a  satur- 
ated alcoholic  solution  of  methylene  blue  (zinc  chloride  double 
salt)  to  195  c.c.  of  distilled  water;  it  should  be  boiled  every  da^^ 
before  using.  One  c.c.  of  the  reagent  is  mixed  with  20  c.c.  of 
milk,  the  surface  is  sealed  with  paraffin,  and  then  the  test-tube 


250  LABORATORY   WORK 

and  its  contents  are  placed  in  a  water-bath  at  45"  C.  to  50°  C. 
Fresh  milk  should  remain  blue  for  twelve  hours  or  more.  The 
reduction  of  methylene  blue  by  raw  milk  (in  the  absence  of 
formalin)  is  due  to  bacterial  contamination,  and  if  the  milk 
decolorizes  within  one  hour  the  organisms  certainly  exceed 
500,000  per  c.c. 

Bacteriological  Note. 

Milk  as  secreted  is  free  from  organisms,  but  even  in  the  milk 
cistern  of  the  udder  and  in  the  teat  canals  some  bacterial  infection 
takes  place ;  while  at  every  stage,  from  the  udder  to  the  consumer, 
contamination  with  bacteria  is  possible,  and  under  many  of 
the  conditions  which  now  prevail  is  invited.  Organisms  gaining 
access  to  milk,  unlike  those  in  air  and  water,  are  usually  in 
an  environment  most  favourable  to  multiplication,  and  as  a 
consequence  milk  as  vended  frequently  contains  one  to  five 
millions  or  more  organisms  per  c.c. ;  the  number,  as  is  to  be 
expected,  being  considerably  greater  in  hot  weather. 

Park*  has  shown  that  in  New  York,  "  with  only  moderate 
cleanliness,  such  as  can  be  employed  by  any  farmer  without 
adding  appreciably  to  his  expense,  namely,  clean  pails,  straining- 
cloths,  cans  or  bottles,  and  hands  ;  a  fairly  clean  place  for  milking, 
and  a  decent  condition  of  the  cow's  udder  and  the  adjacent  belly; 
milk  when  first  drawn  will  not  average  in  hot  weather  over 
30,000  and  in  cold  weather  not  over  25,000  bacteria  per  c.c. 
Such  milk,  if  cooled  to  and  kept  at  50°  F.,  will  not  contain  at 
the  end  of  twenty-four  hours  over  100,000  bacteria  per  c.c.  If 
kept  at  40°  F.  the  number  of  bacteria  will  not  be  over  100,000 
after  forty-eight  hoiirs." 

The  estimation  of  the  number  of  bacteria  in  milk,  or  of  some 
special  group  of  bacteria  such  as  the  B.  coli  group,  is  the  natural 
measure  of  the  degree  of  contamination  of  milk,  but  the  question 
of  the  numbers  to  allow  is  beset  with  difficulties,  largely  owing 
to  the  suitability  of  milk  as  a  medium  for  the  propagation  of 
bacteria. 

A  milk  initially  comparatively  pure  will  frequently  show  after 
the  lapse  of  twelve  to  twenty  hours  many  more  bacteria  than  one 
collected  under  much  less  cleanly  conditions,  and  initially  much 
more  heavily  charged  with  bacteria,  but  examined  after  the  lapse 
of  only  three  or  four  hours  from  milking. 

*  Journal  of  Hygiene,  1901,  vol.  i.,  p.  391. 


BACTERIOLOGICAL   NOTE 


251 


These  differences  in  the  bacterial  content  are  not  only  deter- 
mined by  the  initial  contamination  and  by  the  time  since  milking, 
but  also  by  the  temperature  at  which  the  milk  has  been  kept, 
and  the  latter  introduces  a  condition  subject  to  great  variation. 

The  milk  should  be  collected  in  sterile  glass-stoppered  bottles. 
Those  used  for  the  bacteriological  examination  of  water  may  be 
used,  or  the  simple  and  efficient  apparatus  described  by  Delcpine 
may  be  employed. 

It  consists  of  a  metal  case  containing  a  7  or  8  ounce  bottle  and 
a  milk-scoop.  All  the  parts  are  thoroughly  sterilized  in  the 
laboratory  before  being  sent  out,  and  the  sterilized  case  is  opened 
only  at  the  time  when  the  sample  is  taken.  The  sterilized  scoop 
is  used  to  remove  the  milk  from  the  cans  or  other  vessels.  When 
obtained  direct  from  a  suspected  cow,  the  milk  may  be  milked 


FIG.  38. — delepine's  milk-collecting  apparatus. 

into  the  scoop.  The  metal  cases  are  packed  in  refrigerating 
boxes  if  necessary. 

If  the  sample  cannot  be  examined  within  an  hour  or  so,  it 
must  be  transmitted  packed  in  ice. 

If  milk  from  individual  cows  is  being  collected,  the  teats  and 
the  milkers'  hands  should  be  washed  and  disinfected.  In  some 
cases  it  is  necessary  to  collect  a  separate  sample  from  each 
quarter,  while  for  a  complete  examination  fore,  middle,  and  end 
milk  samples  should  each  be  collected. 

As  a  rule  condensed  milks  are  free  from  preservatives.  In 
the  sweetened  milks  the  sugar  is  sufficient  to  inhibit  the  growth 
of  bacteria,  and  in  the  unsweetened  the  milk  has  been  sterilized 
at  temperatures  over  100°  C.  The  processes  carried  out  in  con- 
densing the  milk  are  sufficient  to  destroy  Bacillus  coli,  B.  tuber- 


252  LABORATORY    WORK 

culosis,  and  other  pathogenic  organisms,  but  spore-bearing 
bacilh,  streptococci,  sarcinae,  yeasts,  and  other  saprophytes,  are 
often  present,  so  that  condensed  milks  must  not  be  regarded  as 
necessarily  sterile.  It  is  probable  that  the  bulk  of  the  organisms 
present  have  gained  admission  during  the  processes  of  cooling 
and  of  filling  the  tins. 

At  the  temperature  of  about  lo^  C.  the  multiplication  of  lactic 
acid  forming  bacteria  is  checked,  and  those  organisms  are  de- 
stroyed at  a  temperature  of  70°  C  maintained  for  twenty  minutes. 
The  ferments  hitherto  detected  in  cow's  milk  (peroxidase,  reduc- 
tase, catalase,  etc),  are  mainly  derived  from  bacteria;  but  certain 
of  such  ferments  which  are  found  to  be  present  in  uncontamin- 
ated  milk,  such  as  amylase,  do  not  appear  to  be  of  value  in  diges- 
tion and  nutrition.  The  chief  enzymes  are  destroyed  at  about 
70°  C.  in  thirty  minutes.  At  80°  C  all  enzymes  are  destroyed; 
but  at  60°  C.  their  activity  is,  if  anything,  slightly  promoted. 

The  discovery  by  Ehrlich  that  passive  immunity  could  be 
produced  by  suckhng  when  the  mother  was  immune,  led  to  the 
investigation  of  the  presence  in  milk  of  precipitins,  agglutinins, 
opsonins,  antitoxins,  and  other  so-called  "  protective  substances  " 
in  milk.     These  are  all  destroyed  at  about  60°  C. 

There  are  also  present  in  milk  certain  biological  bodies  (hor- 
mones and  vitamines)  produced  by  the  direct  action  of  living 
cells.  As  it  appears  that  these  biological  bodies  are  not  absorbed 
in  the  alimentary  canal,  it  is  not  hkely  that  they  act  as  antigens 
in  the  infant.  The  vitamine  present  is  not  destroyed  at  the 
temperature  of  boihng  milk. 


CHAPTER  IV 

BUTTER— CHEESE— LARD 

Butter. 
An  average  sample    of    fresh  butter  has  the  following  com- 
position: 

Fat,  83-5  per  cent. 

Curd  (casein),  i  per  cent. 
Ash,  1-5  per  cent. 
Milk-sugar,  i  per  cent. 
"Water,  13  per  cent. 

The  water  may  vary  from  8  to  15  per  cent. 

The  butter-fat  is  a  combination  of  glycerol  with  certain  fatty 
acids ;  and  consists  of — 

{a)  The  glycerides  of  certain  volatile  fatty  acids,  soluble  in  hot 
water— i.<?.,  principally  butyric,  but  also  smaller  quantities  of 
caproic,  capric,  and  capryUc  acids. 

(b)  The  glycerides  of  certain  fatty  acids,  insoluble  in  hot  water 
—i.e.,  palmitic,  stearic,  oleic,  and  myristic  acids. 

The  glycerides   contain  several   acid  radicles   in    the    same 

molecule. 

The  Butter  and  Margarine  Act,  1907,  requires  that  a  hmit  of 
16  per  cent,  of  water  shall  not  be  exceeded  in  butter  and  mar- 
garine, with  the  exception  of  "  milk-blended  "  butter,  which  may 
contain  24  per  cent. ;  but  the  latter  may  only  be  sold  by  a  name 
which  is  approved  by  the  Board  of  Agriculture  as  not  suggestive 
of  butter. 

It  is  desirable  to  proceed  with  the  analysis  of  butter  without 
delay,  and  if  it  has  to  be  kept  it  should  be  stored  in  a  cool,  dark 
place  pending  analysis ;  for  so  soon  as  butter  commences  to  under- 
go decomposition,  some  of  the  characteristics  which  distinguish 
true  butter-fat  from  other  fats  become  less  marked.     On  becom- 

253 


254  LABORATORY   WORK 

ing  rancid,  the  insoluble  fatt}-  acids  tend  to  increase,  and  the 
soluble  fatt}^  acids  to  diminish.  Rancidity  of  butter-fat  is 
brought  about  by  micro-organisms  in  the  presence  of  light  and 
air,  and  it  spreads  from  the  outside  inwards.  It  sets  in  early 
when  the  butter-milk  is  not  properly  washed  out. 

The  portion  to  be  analyzed  should  not  be  wrapped  in  paper 
(which  will  absorb  moisture),  but  should  be  placed  in  a  clean 
dry  bottle,  carefully  sealed. 

Physical  Characters. — The  odour  and  taste  of  good  butter  are 
familiar  to  everyone,  and  are  so  characteristic  that  they  form 
in  themselves  useful  evidence  of  its  purity.  If  butter  is  heated 
to  21°  C,  an}^  unusual  taste  becomes  more  appreciable. 

\\'ith  regard  to  the  colour,  the  same  remarks  made  in  con- 
nection with  the  colour  of  milk  apply  to  the  butter  made 
from  it. 

The  water,  fat,  curd  and  salt  in  butter  may  be  estimated  as 
follows : 

Weigh  5  grammes  of  butter  into  a  weighed  flat-bottomed 
dish,  and  place  for  about  three  hoiirs  in  a  drying-oven  at  105°  C. ; 
then  cool  and  reweigh,  and  the  loss  represents  water.  Or 
2*5  grammes  of  butter  may  be  placed  in  a  tared  flat-bottomed 
beaker,  and  put  into  the  hot-air  oven  for  several  hours  at  a  tem- 
perature not  exceeding  105°  C — until  no  more  globules  of  water 
can  be  seen  on  looking  at  the  glass  beaker  from  below,  and  until 
a  constant  weight  is  obtained.  The  fat  may  be  estimated  by 
extracting  the  water-free  butter  with  ether.  The  washing  should 
be  repeated  several  times  with  fresh  ether  (which  is  decanted 
cautiously  after  each  washing) ;  the  residue  is  then  dried  and 
weighed,  and  thus  the  weight  of  curd  and  salt  is  obtained,  and 
from  the  loss  in  weight  the  fat  is  estimated.  The  salts  may  be 
weighed  after  incinerating  the  fat-free  residue  at  as  low  a  tem- 
perature as  possible. 

Adulteration. — All  foreign  fats  made  up  to  resemble  butter, 
and  whether  mixed  with  butter  or  not,  have  now  to  be  labelled 
and  sold  as  "  margarine." 

In  the  manufacture  of  oleo-margarine  animal  and  vegetable 
fats  are  melted,  strained,  cooled  with  ice,  worked  up  with  a  little 
milk,  artificially  coloured  and  salted;  the  result  is  an  article  very 
similar  in  appearance  and  taste  to  ordinary  butter,  and  but  little 
inferior,  if  at  all,  in  nutritive  qualities.  It  constitutes  a  good 
article  of  food,  but  it  must  be  labelled  and  not  sold  as  butter. 


TBtTTTER 


255 


Lard,  beef  and  mutton  fats,  together  with  vegetable  oils  (cotton- 
seed, sesame,  cocoa-nut,  earth-nut),  have  been  employed  as  sub- 
stitutes of  butter-fat.  Paraffin  or  petroleum  oil  and  solid  paraffm- 
wax  have  rarely  been  incorporated  with  margarine.  Paraffin 
has  no  food  value,  and  it  is  liable  to  prove  deleterious  to  health. 
Some  control  is  needed  over  the  oils  employed  in  the  manufacture 
of  margarine. 

The  lines  upon  which  to  proceed  in  order  to  detect  whether  the 
sample  consists  of  pure  butter-fat,  an  admixture  of  this  with 
other  fats,  or  of  these  prepared  foreign  fats  alone,  must  be  those 
which  take  advantage  of  the  differences  existing  in  the  composi- 
tion of  the  fats. 

The  following  are  important  differences : 


Butter-Fat. 

1.  The  specific  gravity  at  38°  C. 
is  extremely  rarely  below  910,  and 
never  below  909-8. 

2.  The  soluble  volatile  fatty  acids 
form  between  6  and  7  per  cent,  on 
an  average,  and  are  never  below  4"5. 

The  insoluble  fatty  acids  form 
about  88  per  cent. 

3.  The  Reichert  -  Wollny  figure 
(5  grammes)  is  from  about  24  to  32.* 

4.  By  the  Valenta  test  the  fat 
clears  at  30°  to  40°  C. 

5.  Polariscope.  —  When  a  thin 
layer  of  the  sample  is  examined 
by  the  micro-polariscope,  at  the 
moment  the  Nicol  prisms  are 
crossed,  the  whole  field  is  dark, 
except  for  a  few  minute  specks  due 
to  preservatives,  etc. 


The  Other  Fats  most  used 
AS  Substitutes. 

1.  Never  above  904  in  margarine 
from  beef  or  mutton  fat,  but  is 
higher  where  vegetable  fats  are 
employed. 

2.  Constitute  rarely  more  than 
5  per  cent.,  and  never  more  than 
f  per  cent. 

Generally  about  95  per  cent. 

3.  The  figure  is  generally  from 
I  to  2,  except  in  respect  of  cocoa- 
nut  oil,  when  it  is  from  7  to  8. 

4.  No  animal  fats  clear  below 
94°  C,  and  no  vegetable  oil  used  as 
a  substitute  clears  below  80°  C. 

5.  Similarly  treated,  any  mix- 
ture containing  more  than  40  per 
cent,  of  foreign  fat  shows  a  field 
full  of  light,  cloud-like,  forms.  In 
fact,  it  is  impossible  to  get  a  dark 
field.  Since  mixtures  of  butter 
and  margarine  are  rare,  this  is  the 
best  physical  test.  It  really  shows 
that  the  fat  used  has  been  melted. 


Supposing  the  specific  gravity  is  found  to  be  907,  then,  if  we 
take  the  lowest  specific  gravity  of  pure  butter  as  gio,  the  per- 
centage amount  of  foreign  fat  in  the  sample  may  be  roughly 
gauged. 

*  Some  pure  Irish  butters  have  furnished  figures  of  between  20  and  24. 


256  LABORATORY   WORK 

910=  the  lowest  specific  gravity  of  pure  butter-fat. 

904=  the  highest  specific  gravity  of  other  animal  fats. 

If,  therefore,  the  specific  gravity  is  as  much  as  6  below  910, 
this  would  indicate  100  per  cent,  of  adulteration,  or  that  none  of 
the  material  was  butter-fat. 

The  sample  has  a  specific  gravity  of  907,  and  therefore  3  below 
910,  which  will  represent  (6:3::  100  :  x)  50  per  cent,  of  adultera- 
tion with  foreign  fat. 

The  specific  gravity  of  cotton-seed  oil  is  above  912. 

But  by  far  the  best  evidence  of  the  presence  of  foreign  fat  is 
derivable  from  the  amount  of  soluble  and  volatile  fatty  acids 
present ;  and  this  is  best  obtained  by  the  following  method  : 

The  Reichert-Wollny  Process. — The  volatile  and  soluble  fats 
have  been  seen  to  be  relativel}'  much  higher  in  butter-fat  than  in 
the  other  fats  used  as  substitutes.  If,  then,  the  volatile  fatty 
acid  is  separated,  the  acidity  which  it  furnishes  in  the  case  of 
butter-fat  will  be  considerably  greater  than  any  acidit}-  furnished 
by  other  fats  similarly  treated. 

1.  The  recently  melted  butter-fat,  filtered  through  a  dry  filter, 
is  poured  into  a  weighed  small  -  necked  glass  flask  {200  c.c. 
capacity)  until  the  scales  register  the  addition  of  5  grammes  of 
butter-fat  at  about  38°  C.  If  fat  in  slight  excess  of  this  weight  is 
added,  the  excess  may  be  removed  by  a  glass  rod,  and  with  a  little 
care  it  is  not  difficult  to  weigh  out  precisely  5  grammes. 

2.  Two  c.c.  of  a  50  per  cent,  soda  solution,  and  10  c.c.  of 
about  92  per  cent,  alcohol,  are  then  added  to  the  flask,  which  is 
fitted  with  a  vertical  glass  tube  to  act  as  a  reflux  condenser; 
it  is  then  placed  on  a  water-bath  and  heated  for  a  quarter  of  an 
hour,  the  flask  being  gently  rotated  from  time  to  time.  Soaps  are 
thus  formed  by  the  combination  of  the  fatty  acids  with  the 
alkali. 

The  cork  and  tube  are  now  removed,  and  the  alcohol  distilled 
off  while  the  flask  is  heated  for  about  half  an  hour,  or  until  the 
soap  is  dry.  Any  traces  of  alcohol  remaining  in  the  flask  can  be 
removed  by  sucking  the  air  out  through  a  narrow  tube  passed 
through  a  cork  inserted  in  the  flask. 

3.  One  hundred  c.c.  of  hot  distilled  water,  which  has  been  kept 
boiling  for  ten  minutes,  are  next  added,  and  the  whole  gently 
heated,  with  occasional  shakings,  until  the  soap  is  completely 
dissolved. 


BUTTER 


257 


4.  Forty  c.c.  of  dilute  sulphuric  acid  (i  in  40)  are  poured  in 
after  the  soap  solution  has  cooled  to  about  62"'  C. ;  the  soap  is  thus 
decomposed,  and  the  fatty  acids  are  set  free. 

The  flask  is  restoppered,  when  the  fatty  acid  emulsion  is  fused 
by  a  gentle  heat,  and  then  allowed  to  cool. 

5.  Two  pieces  of  pumice  of  the  size  of  a  pea  are  added  to 
prevent  bumping,  and  the  flask  is  then  connected  to  a  small 
condensing  apparatus  by  means  of  a  glass  tube  7  millimetres 
wide  and  having  at  a  distance  of  5  centimetres  above  the  cork  a 
bulb  of  a  diameter  of  5  centimetres ;  the  tube  is  bent  immediately 
over  the  bulb  upwards  in  an  oblique  angle,  in  which  direction  it 
extends  for  5  centimetres,  and  is  then  again  bent  downwards, 
also  obliquely.     Connection  is  made  with  a  condenser  by  means 


FIG.    39. APPARATUS    FOR    THE    REICHERT-WOLLNY    PROCESS. 

of  an  india-rubber  tube,  and  the  contents  of  the  flask  are  gradually 
heated  and  made  to  boil  slowly.  The  insoluble  fatty  acids  are 
melted  and  the  butyric  acid  is  distilled  over  unchanged ;  but  the 
distillate  also  contains  some  of  the  insoluble  volatile  fatty*  acids, 
and  these  must  be  separated  by  allowing  the  distillate  to  run 
through  a  dry  filter  before  it  is  finally  collected. 

6.  Exactly  no  c.c.  of  the  filtered  distillate  are  collected  in  a 
graduated  flask  (the  flame  being  regulated  in  such  a  way  that 
the  distillation  lasts  thirty  minutes),  and  the  acidity  of  the 
distillate  is  estimated  by  means  of  a  decinormal  solution  of  an 
alkali  (baryta  best),  phenolphthalein  being  used  as  indicator. 
To  the  figure  thus  obtained  the  amount  found  by  a  blank  experi- 
ment with  the  alcoholic  soda  solution  (made  at  the  same  time 

17 


258 


LABORATORY   WORK 


and  under  precisely  similar  conditions)  is  subtracted.  This 
deduction  ought  not  to  amount  to  more  than  0-3  c.c.  of  the 
Ys  alkali.  The  result  is  known  as  the  "  Rcichert-Wollny 
number." 

Five  grammes  of  pure  butter-fat  treated  in  this  manner  do 
not  yield  a  less  amount  of  acidity  than  corresponds  to  a  Reichert- 
Wollny  number  of  24*  (24  c.c.  of  decinormal  soda  or  baryta 
solution),  and  the  "  number  "  may  be  from  24  to  32.  Oleo- 
margarine furnishes  a  number  generally  from  i  to  2,  as  a  little 
milk  is  usually  churned  in  to  give  a  butter  flavour  and  this 
may  account  for  as  much  as  5  to  6  per  cent,  of  butter-fat.  In 
this  country,  in  order  to  make  the  practice  of  fraud  more  diffi- 
cult and  its  chemical  detection  more  easy,  more  than  10  per 
cent,  of  butter-fat  in  margarines  is  prohibited  by  the  Sale  of 
Food  and  Drugs  Act,  1899.  This  amount  of  butter-fat  in 
margarine  will  furnish  a  Reichert-Wollny  number  of  four. 

The  Society  of  Public  Analysts  has  decided  that  the  amount 
of  butter-fat  in  margarine,  when  it  exceeds  the  legal  limit  of 
10  per  cent.,  shall  be  assumed  to  be  as  follows: 


Rcichert-Wollny  Number 
of  the  Mixture. 

Percentage  of  Butter-Fat 
present  in  the  Mixture. 

4-0 

10 

4-3 

II 

4-6 

12 

4.9 

13 

5-2 

14 

5-5 

15 

5-9 

16 

6-2 

17 

6-5 

18 

6-8 

19 

7-1 

20 

Supposing  the  Reichert-Wollny  figure  is  20  c.c,  what  would  be 
the  percentage  of  pure  butter-fat  in  the  sample  ?  Taking  2  as 
the  highest  possible  figure  for  other  fats  (in  the  absence  of  cocoa- 
nut  oil),  and  24  as  the  lowest  figure  for  butter-fat,  a  difference  of 
22  {24-2)  would  represent  100  per  cent,  of  genuine  butter. 
The  per  cent,  of  genuine  butter  in  a  mixture  with  a  figure  of  20 
would  be  represented  by  (20  -2)  18.     Now  if  22  =100  per  cent. 

*  Some  pure  Irish  butters  have,  however,  furnished  figures  of  between 
20  and  24. 


BUTTEli  25g 


t!ZlVT''T  '.^-^^P^"^"'-;^""  100-82.18  per  cent,  of 
tlie  total  lat  is  foreign. 

_  Nole.~By  means  of  a  T-piece  in  tlio  tube  by  whicli  the  flask 
IS  connected  with  the  condenser,  the  alcohol  cfn  be  distilled  off 
and  water  added  to  the  residual  soap  without  opening  the  flask 
and  exposing  the  contents  to  the  CO^  of  the  air 

Leffmann  and  Beam  substitute  a  solution  of  sodium  hydrate  in 
glycero  for  the  alcohol  and  sodic  hydrate  used  as  the  saponTfy  ng 
agent,  this  dispenses  with  the  use  of  alcohol,  and  so  prevents 
the  results  bemg  vitiated  by  the  absorption  of  Cof  dlw 
evaporation,  and  it  shortens  the  time  required  for  the  process 
The  solution  is  made  by  allowing  a  so'per  cent.  soluC  of' 

^:^.:^^.::z^:^^  --  --  -  --- 

Polenske  has  modified  the  process  in  a  way  which  increases 

::ii  i^tttt  • '''  ^^^^°^^ ''  '^'^'''^^  ^^^  ~^  ^^  -cor: 

I.  When  the  no  c.c.  of  distillate  have  been  collected  the 
receiver  is  replaced  by  a  25  c.c.  cylinder  ' 

2  Without  mixing  its  contents,  the  receiver  is  now  placed  in 
a  bath  of  water  at  10°  C.-the  water  surface  of  which  ^omes  o 
the  level  of  the  no  c.c.  mark,  or  just  above  it 

3.  The  msoluble  fatty  acids  rise  to  the  surface  in  the  receiver- 
and  in  the  case  of  butter  they  form  a  solid  mass  of  wh  te  opTque 
granules    whilst  with  pure   cocoanut   oil   only  oily  dropfare 
obtained      Mixtures  containing  more  than  10  per  cent  of Tocoa 
nut  oil  also  yield  oily  droplets. 

4.  After  mixing  and  filtering  the  contents  of  the  receiver,  the 
Reichert  value  is  determined  on  the  filtrate 

5.  The  condenser-cylinder  and  receiver  are  washed  with  18  c  c 
of  water,  which  are  then  poured  over  the  filter 

6    rhe  msoluble  fatty  acids  on  the  filter  are  now  dissolved  in 

1       'iT.'i'''  "'-"^"^  '"''^''^  "^^^  B-(OH),  solu  Sn  "sing 
phenolphthalein  as  indicator.  ^ 

7.  The  numi^r  of  c.c.  of  ^  barium  liydroxide  solution  required 
.s  termed  the  •■  new  butter  value  "  of  the  fat  under  exammat  on 
Genu.„e  b,«er  does  not  g.ve  "new  butter  values"  exc    di 


mg  3-0 


Witt  RettrtV'  ™™r"'  °"  -""^^^  ""'^  fig"--  -  ™-»-t  oil 


260  LABORATORY   WORK 

If  3  c.c.  of  the  melted  fat  is  mixed  with  3  c.c.  of  glacial  acetic 
acid  (S.G.  1056-2)  in  a  narrow  graduated  tube  and  a  thermometer 
inserted,  it  will  be  seen  that  margarine  docs  not  form  a  cleai" 
solution  when  the  mixture  is  warmed  and  well  shaken  up  until 
a  temperature  of  94°  C.  is  reached,  but  butter  generally  clears  at 
about  36°  C.  (Valenta  test).  Genuine  butter  samples  vary  some- 
what as  to  the  temperature  at  which  they  clear,  and  the  variation 
falls  between  30°  and  40°  C;  but  no  animal  fats  clear  below 
94°  C,  and  no  vegetable  oil  of  conunon  use  clears  below  80°  C. 
The  test  may  be  applied  by  discontinuing  the  heat  after  complete 
solution  has  taken  place,  retaining  the  thermometer  in  the  solu- 
tion, and  taking  the  temperature  at  which  the  liquid  becomes 
turbid.  The  clarifying  temperature  is  taken  as  half-way  between 
that  noted  when  the  mixture  first  cleared  and  that  when  the 
mixture  commenced  to  become  turbid  again. 

Jean  has  extended  the  test  as  follows:  After  a  few  minutes 
it  is  seen  how  much  acetic  acid  has  separated  out,  since  some  of 
the  acid  is  absorbed  by  the  fat.  Suppose  the  level  of  the  acetic 
acid  after  the  experiment  was  i-i  c.c,  then  the  acetic  acid 
absorbed  by  the  butter  =  3  — i-i=  1-9  c.c,  and  1-9  c.c.  in  3  cc  = 
63  per  cent.  Butter-fat  absorbs  over  60  per  cent.,  while  the 
fat  of  margarine  rarely  absorbs  over  30  per  cent. 

A  useful  rough  test  for  margarine  is  to  add  5  grammes  of  the 
fat  to  50  c.c.  of  fresh  milk,  which  has  been  heated  ahnost  to  the 
boiling-point,  and  stir  the  mixture  with  a  wooden  stick  imtil 
the  fat  is  melted.  Then  place  the  beaker  in  ice-cold  water,  and 
continue  stirring  until  the  solidifying  point  of  the  fat  is  reached. 
If  the  sample  is  margarine,  the  fat  can  be  collected  into  a  rela- 
tively hard  lump;  but  if  it  is  butter,  the  mass  is  soft  and  creamy 
in  consistence,  or  the  fat  is  more  or  less  distributed  throughout 
the  milk. 

Margarine  may  be  suspected  if  on  burning  a  small  portion  of 
the  substance  on  a  clean  platinum  spatula,  the  peculiar  odour  of 
burnt  tallow  is  given  off,  after  extinguishing  the  flame. 

When  butter  is  heated  in  a  platinum  dish  over  a  gas-burner 
it  foams  considerably,  and  may  run  over  the  dish;  but  there  is 
less  noisy  spluttering  than  is  commonly  the  case  with  margarine, 
and  there  is  less  foaming  with  the  latter. 

An  alcoholic  solution  of  sodic  hydrate  warmed  with  butter  and 
then  emptied  on  to  cold  water  gives  a  distinct  odour  of  pineapple; 
not  so  with  margarine. 


BUTTER  261 

Butter-fat  is  readily  and  completely  soluble  in  ether;  margarine 
is  frequently  less  so,  and  it  may  deposit  a  residue. 

Admixture  with  small  quantities  of  certain  fats  is  practically 
unrecognizable  by  any  of  the  tests  already  given.  The  following 
direct  tests  are  of  assistance : 

Cocoanui  Oil.- — The  recent  employment  of  this  oil  in  the  manu- 
facture of  margarine  and  in  the  adulteration  of  butter  has 
diminished  the  value  of  the  indications  of  the  Reichert-Wollny 
method,  for  this  oil  contains  a  comparatively  large  proportion 
of  the  glycerides  of  the  volatile  fatty  acids.  Cocoanut  oil  gives 
a  Reichert-Wollny  figure  of  7,  and  its  presence  in  butter  is  best 
detected  by  the  Polenske  method  {vide  p.  259). 

Cotton-seed  Oil. — Mix  the  oil  with  an  equal  volume  of  a  satur- 
ated solution  of  plumbic  acetate,  add  ammonia  and  stir  quickly ; 
the  surface  turns  an  orange-red  upon  standing.  This  test  readily 
detects  10  per  cent.  A  slight  reaction  of  cotton-seed  oil  may  be 
due  to  the  cows  feeding  on  cake  or  meal  containing  this  oil.  It 
may  be  noted  that  this  oil  has  a  very  high  specific  gravity.  The 
silver  test  (Bechi)  is  a  good  one:  i  gramme  of  silver  nitrate  is 
dissolved  in  100  c.c.  of  95  per  cent,  alcohol,  and  then  20  c.c.  of 
ether  and  i  drop  of  nitric  acid  are  added;  if  2  c.c.  of  this  reagent 
are  mixed  with  10  c.c.  of  the  oil,  and  the  test-tube  then  stood  in 
boiling  water  for  fifteen  minutes,  the  contents  darken  in  the  pres- 
ence of  cotton-seed  oil.    The  blackening  is  due  to  reduced  silver. 

Halphen's  test :  Mix  with  an  equal  volume  of  fusel  oil,  carbon 
bisulphide  containing  2  per  cent,  of  sulphur  in  solution;  3  c.c.  of 
this  mixture  are  added  to  3  c.c.  of  the  oil,  mixed  and  heated  in 
a  bath  of  boiling  brine  for  fifteen  minutes.  If  no  reddish  tint 
is  produced,  add  another  i  c.c.  of  the  reagent,  and  if  after  five 
minutes'  heating  no  colour  develops,  further  add  i  c.c.  of  reagent 
before  deciding  that  no  cotton -seed  oil  is  present.  For  quanti- 
tative purposes,  the  colour  may  be  matched  against  standard 
colours  obtained  from  oils  containing  known  amounts  of  cotton- 
seed oil. 

Earth-nut  Oil. — ^As  little  as  i  per  cent,  furnishes  a  dark  brown- 
ish-red colour  with  concentrated  sulphuric  acid,  whereas  pure 
butter  gives  a  straw-yellow  to  a  reddish-yellow  colour. 

Sesame  Oil. — Dissolve  o-i  gramme  of  cane-sugar  in  10  c.c.  of 
HCl  (S.G.  I  125),  then  add  20  c.c.  of  the  fat;  shake,  and  let  stand; 
a  crimson  colour  appears  if  sesame  oil  is  present.  Or  the  test 
may  be  applied  by  substituting  a  o-i  c.c.  solution  of  furfural  for 


262  LABORATORY    WORK 

the  cane-sugar.  Fats  containing  sesame  oil  give  a  pennanent, 
fine  red  colour  when  heated  on  a  water-bath  with  stannous 
cliloride,  and  the  colour  is  not  discharged  by  moderately  diluting 
with  water.  Turmeric  also  gives  a  reddish  coloration  with  strong 
hydrochloric  acid  or  stannous  chloride,  but  the  colour  is  not 
stable,  and  disappears  on  adding  water.  The  oil  has  a  high 
specific  gravity. 

Annatto,  and  more  rarely  turmeric,  saffron,  marigold,  carrotin, 
and  certain  coal-tar  colours,  are  used  as  colouring  agents;  their 
presence  may  be  detected  by  shaking  up  about  5  grammes  of  the 
melted  and  filtered  butter,  in  a  tube,  with  25  c.c.  of  a  mixture 
of  15  parts  of  methylic  alcohol  and  2  of  carbon  bisulphide;  the 
fat  dissolves  in  the  carbon  bisulphide,  and  the  alcohol,  along  with 
the  colouring  matter,  floats  above.  To  ascertain  the  nature  of 
the  agent  employed,  special  tests  must  be  applied,  as  indicated 
in  the  chapter  on  Antiseptics  and  Colouring  Agents  in  Food. 

Boric  acid  is  frequently  found  in  butter  and  cream,  for  it  enters 
in  the  composition  of  proprietary  nostrums  sold  for  preserving 
these  articles.  Salicylic  acid  and  sodium  benzoate  and  fluoride 
have  also  been  employed  as  preservatives  of  certain  French 
butters. 

Water  is  sometimes  worked  into  butter  in  excessive  quantities 
for  fraudulent  purposes,  but  water  much  exceeding  16  per  cent, 
reduces  the  keeping  powers  of  the  butter.  Most  margarines 
contain  a  relatively  small  amount  of  water.  Common  salt  is 
added  to  improve  the  flavour,  and  also  to  preserve  the  butter  by 
checking  the  decomposition  of  the  casein ;  rarely  does  the  per- 
centage amount  exceed  that  which  will  lend  a  palatable  amount 
of  saltness  to  the  butter — i.e.,  about  5  or  6  per  cent. 

Butter  occasionally  contains  the  BaciUus  tuberculosis  and 
other  acid-fast  organisms ;  and  bacteria  determine  its  flavour. 


Cheese. 

Cheese  consists  of  the  original  constituents  (chiefly  the  casein 
and  fat)  of  the  milk  (cows  or  goats)  from  which  it  is  made ;  but, 
as  ripening  proceeds,  the  sugar  becomes  transformed  (chiefly  into 
lactic  acid),  and  the  decomposition  is  accompanied  by  a  diminu- 
tion of  fat  and  a  considerable  growth  of  bacteria,  fungi,  moulds, 
etc.     There  is  no  legal  standard  applying  to  cheese  in  this  country. 

The  water,  though  higher  in  Dutch  cheese  and  lower  in  Stilton 


CHEESR 


263 


and  American,  averages  from  32  to  35  per  cent. ;  the  fat  commonly 
varies  from  30  to  40  per  cent.,  but  is  considerably  lower  (12  to 
22  per  cent.)  in  Dutch  cheese,  which  is  made  from  partially 
skimmed  milk;  the  casein  is  commonly  from  28  to  33  per  cent.; 
and  the  ash  is  usually  about  4  per  cent.,  but  may  exceed  6  per 
cent,  in  Dutch  cheese.  The  water  in  cream  cheeses  often  exceeds 
50  per  cent. 

There  is  comparatively  little  adulteration  practised  in  the 
manufacture  of  cheese.  For  the  curd,  which  is  separated  from 
milk  by  rennet,  there  is  no  spurious  and  cheap  substitute  which 
can  be  made  to  yield  the  peculiar  characters  of  pure  cheese; 
but  animal  and  vegetable  fats  are  employed  in  the  manufacture 
of  "  margarine  cheese  "  and  in  the  adulteration  of  the  cheaper 
cheeses.  The  substance  known  as  "  filled  cheese  "  is  prepared 
from  skimmed  milk,  lard,  and  other  fats.  Very  little  "  margarine 
cheese  "  is  sold  in  this  country. 


FIG.  40. ASPERGILLUS  GLAUCUS.   (  X  ABOUT  200.) 

It  has  been  shown  that  in  some  cases  (especially  of  foreign 
cheeses)  the  surfaces  have  been  brushed  over  with  highly  poison- 
ous antiseptic  solutions,  such  as  arsenious  acid  and  sulphate  of 
copper,  in  order  to  preserve  them ;  that  colouring  matters  (lead 
chromate,  etc.)  have  also  been  used  to  tint  the  rind;  and  that 
those  small  and  delicate  cheeses  which  are  wrapped  in  thin  lead 
papers  may  take  up  the  metal.  A  careful  examination,  therefore, 
of  the  rind  for  metallic  poisons  may  occasionally  be  desirable. 

The  total  solids  and  the  water  may  be  determined  by  prolonged 
drying  in  an  air-bath  of  about  i  gramme  of  the  finely  scraped 
cheese,  until  a  constant  weight  is  obtained. 

The  fat  may  be  estimated  by  boiling  a  known  weight  of  the 
dried  cheese  in  a  small  flask  with  a  quantity  of  strong  hydro- 
chloric acid.  When  it  is  all  dissolved,  the  flask  is  cooled  and  the 
contents  extracted  with  ether  three  times.    The  separated  ether 


264 


LABORATORY    WORK 


is  now  evaporated  off  from  the  flask  to  which  it  has  been  trans- 
ferred, and  the  residual  fat  is  dried  and  weighed.  A  deficiency 
of  fat  would  be  indicated,  and  suspicion  warranted,  if  a  cheese, 
other  than  Dutch  cheese,  contained  less  than  30  per  cent,  of  fat. 

The  proteid  matter  is  ascertained  l)y  multiplying  the  nitrogen 
figure  by  6-38. 

The  purity  of  the  fat  is  ascertained  by  the  Reichert-Wollny 
method  of  examination.  The  fat  is  easily  extracted  by  boiling 
some  shredded  cheese  with  strong  hydrochloric  acid  in  a  flask 
and  then  washing  the  fat  in  a  separating-funnel  with  hot  water. 


FIG.  41. MUCOR  MUCEDO. 

(X  ABOUT  200). 


FIG.   42.  THE   CHEESE 

MITE  (ACARUS  DOMESTI- 
CUS).   (X  ABOUT  40.) 


In  genuine  cheese  the  Reichert-\\'olln\'  figure  of  the  fat  exceeds 
18,  whereas  "  margarine  cheese  "  gives  a  figure  which  is  generally 
below  6. 

The  action  of  ferments,  etc.,  on  the  fat  of  cheese  usually 
reduces  the  Reichert-Wollny  figure;  the  "  riper  "  the  cheese  the 
lower  this  figure. 

Cheese  is  peculiarly  liable — and  especially  the  moister  kinds — 
to  parasitic  growths.  Aspergillus  glauciis  is  a  form  of  vegetable 
fungus,  which  gives  rise  to  the  appearance  popularly  known  as 
"  blue  mould,"  and  sometimes  also  to  "  green  mould  " ;  under  the 
microscope  its  appearance  is  that  denoted  in  Fig.  40. 

Sporcndoncma  casei  is  a  similar  growth,  furnishing  the  appear- 
ance known  as  "  red  mould."  Mucor  mucedo  (Fig.  41)  is  another 
fungus  which  attacks  cheese, 


LARD  265 

Acams  domestims,  the  cheese  mite,  is  a  tiny  animal  parasite 
shown  magnified  in  Fig.  42. 

The,  cheese  maggots  are  animal  parasites  of  much  larger  growth; 
they  are  the  larvce  of  a  fly  known  as  Piophila  casei,  and  are  readily 
detected  by  either  the  naked  eye,  or  a  small  hand  lens. 


Lard. 

Lard  is  the  fat  obtained  from  the  interior  of  the  abdomen  of 
swine ;  it  is  considerably  adulterated  with  the  oils  and  fats  that 
are  employed  as  butter  substitutes  (cotton-seed  oil,  cocoanut  oil, 
beef  stearin),  and  with  excess  of  water. 

The  fats  may  be  examined  as  in  butter. 

Paraffin  has  been  found  as  an  adulterant  of  lard.  It  may 
be  detected  by  adding  to  3  c.c.  of  the  melted  fat,  10  c.c.  of  a 
mixture  of  equal  parts  of  absolute  alcohol  and  chloroform,  and 
heating  in  a  water-bath  until  complete  dissolution.  On  cooling 
the  tube  with  water,  the  contents  become  cloudy  if  paraffin  is 
present. 


CHAPTER  V 

CORN— WHEAT-FLOUR 

Corn. 

This  term  includes  the  seeds  of  cereal  plants  in  general.  Certain 
abnormal  conditions  of  the  entire  seed  which  are  brought  about 
by  small  animal  and  vegetable  parasites  claim  consideration. 


FIG.    43. THE    CORN    WEEVIL    (CALANDRA    GRANARIA)  .       (  X  ABOUT    40.) 

Those  seeds  presenting  minute  round  perforations,  and  con- 
sisting almost  entirely  of  a  shell,  have  generally  been  penetrated 
by  a  small  insect,  visible  to  the  naked  eye,  termed  Calandra 
granaria  {vide  Fig.  43),  and  popularl^^  known  as  the  "  weevil." 


FIG.    44. VIBRIONES    TRITICI.        f  X  ABOUT    40.) 

These  parasites  may  also  be  found  in  stored  biscuits,  to  which 
articles  species  of  Lepidoptera,  notably  the  Ephestise,  in  different 
stages  of  development,  have  sometimes  proved  very  destructive. 

Those  which  are  small,  black,  or  discoloured,  and  in  which 

266 


CORN 


267 


the  bulk  of  their  substance  is  replaced  by  ;).  fine  c;ottony  mfi.teria], 
have  been  attacked  by  the  "  ear-cockle,"  or  Vibrio  triiici — a 
small  worm-hke  parasite,  pointed  at  either  end  as  shown  in 
Fig.  44.  They  are  often  to  be  seen  in  considerable  numbers  in 
damp  wheat. 

The  Acarus  farincs  is  a  small  microscopic  parasite  which  infests 
the  grain,  and  closely  resembles  the  Acarus  scabiei.     It  especially 


FIG.    45. A    WHEAT    SPIKELET 

WITH    EAR-COCKLE.        (Xj.) 


FIG.    46.- 


-THE    WHEAT    MITE    (ACARUS 
FARIN/E).       (x  85.) 


affects  damp  and  inferior   flour.     Its   characters   are  shown  in 

Fig.  46.     The  eggs  of  the  parasite  are  oval. 

The  various  fungi  which  attack  corn  are  the  following: 

I.  Claviceps  purpurea  is  a  fungus  chiefly  affecting  rye,  and  the 

mycelial  growth  v/hich  replaces  the  grain  is  known  as  ergot.     In 

the'^spring  of  the  year  small  hair-like  growths  with  a  knob  at  the 


FIG.    47.       (X  ABOUT   250.) 

A,  Ear  of  rye  with  Ergot,  the  latter  shown  as  germinating  and  pro- 
ducing Claviceps  purpurea  ;  B,  a  section  of  ergot. 

free  end  grow  out  from  the  mycelium;  these  are  known  as 
stromata,  the  microscopic  appearance  of  which  is  shown  in 
Figs.  47  and  48.  Each  stroma  contains  near  its  border  a  row 
of  receptacles  (ascocarps),  containing  onion-shaped  bodies,  known 
as  asci.  These  asci  ultimately  get  detached  and  rupture, 
liberating  their  contained  eight  filiform  spores  (ascospores),  to 


268  LABORATORY    WORK 

be  borne  by  the  wind  to  infect  the  ovary  of  the  rye-flower.  The 
fungus  may  cause  a  condition  known  as  "  ergotism  "  among 
many  of  those  who  habitually  consume  rye  bread  and  biscuits. 
Those  seeds  which  are  not  entirely  replaced  by  the  fungus  are 
discoloured  brown  or  purple,  and  the  flour  is  also  discoloured, 
and  generally  furnishes  a  peculiar  sour  odour.     A  microscopic 


Mfl 


FIG.    48. ERGOT. 

Section  of  the  end  of  a  stroma,  showing  ascocaqDS  and  asci. 

examination  shows  a  very  dense  tissue  formed  by  dark  polygonal 
cells  filled  with  oil}'  constituents  (Fig.  47),  and  to  the  naked  eye 
the  ovary  is  black  externally  and  spongy  internally. 

Chemically,  its  presence  in  flour  ma^^  be  detected  by  the  fol- 
lowing methods: 

{a)  The  flour  is  made  into  a  paste  with  a  weak  solution  of 
potassic  hydrate,  and  then  dilute  nitric  acid  is  added 
to  slight  excess.  When  the  whole  is  subsequently 
neutralized  by  a  Httle  more  of  the  potassic  hydrate 
solution,  a  violet-red  colour  forms  if  ergot  is  present, 
and  a  violet  colour  is  established  when  more  of  the 
alkaline  solution  is  added. 


CORN 


269 


(6)  On  the  addition  of  potassic  hydrate  sohition  to  the  flour, 

a  distinct  herring-like  odour  is  appreciable — due  to 

trimcthylaminc. 

(c)  The  flour  is  made  thoroughly  moist  witli  ether,  a  few 

drops  of  dilute  sulphuric  acid  are  added,   and  the 

whole  is  then  weU  agitated ;  on  the  addition  of  a  few 

drops  of  a  saturated  solution  of  sodium  bicarbonate 

a  violet  colour  appears  (Hoffmann). 

2.   Uredo  segetum,  "  smut,"  especially  affects  barley,  rye,  wheat 

and  oats.     The  fine  dark  dust,  which  sometimes  gives  the  ear  of 

wheat  the  appearance  of  having  been  placed  up  the  chimney, 


I     £7  £5  O    O      '^  O    '^ 

'„oO  00   00° 

Q  O      C?  „        (DC? 


FIG     49.— SMUT    SPORES    (uREDO  FIG.    50.— BUNT    (UREDO 

segetum).       (X200.)  FCETIDA).       (X200.) 

is  inodorous,  and  has  suggested  the  popular  name  "  dust  brand  " 
to  the  condition.  Bread  made  with  flour  thus  affected  is  bluish. 
Tilletia  caries  {Uredo  fceti da)  and  Tilletia  Icevis  are  of  the  same 
family  ( UstilaginecB) . 

3.   Uredo  fatida  [Tilletia  caries),  "bunt,"  affects  the  interior 
of  the  grains  of  wheat,  which  it  replaces  by  spores  furnishing  a 


B 
FIG.    51. —  (X  200.) 

A,  Tilletia  caries  (bunt),  showing  germination;  B,  bunt  very  highly  magni- 
fied; C,  Tilletia  Iczvis. 

fine  dust,  and  hence  the  condition  is  sometimes  called  "  pepper 
brand."  The  dust  when  rubbed  between  the  fingers  has  a 
slippery  and  greasy  feel,  and  gives  off  a  peculiar  foetid  odour. 
No  ill  effect  has  been  ascribed  to  the  consumption  of  flour  affected 
with  either  Uredo  fcetida  or  Uredo  segetum.  The  microscopic 
appearance  of  "  bunt  "  is  shown  in  Figs.  50  and  51. 


270 


LABORATORY   WORK 


4.  Puccinia  Graminis.— The  sporangia — as  shown  in  Fig.  52 — 
consist  of  dark,  rounded  masses,  which  show  either  a  double 
hnear  contour  or  one  presenting  numerous  small  projections. 
The  wheat-ear  or  barley  and  rye  ears  and  stalk  attacked  by  this 


r^-. 


FIG.    52. PUCCINIA    GRAMINIS.       (  X  ABOUT    200.) 

fungus  are  more  or  less  covered  by  a  fine  brownish  deposit,  which 
has  been  most  aptly  designated  "  rust." 

5.  Mucor,  aspergilliis,  and  penicillium,  may  also  be  seen  in 
decomposing  com. 

Wheat-Flour. 
At  the  present  day  the  miller  endeavours  to  produce  a  flour 
which  consists  as  nearly  as  possible  solely  of  the  contents  of  the 


graaao^si 


...p 


e- 

772-- 
d- 

a'' 

p— 


FIG.  53. CROSS  SECTION  THROUGH  BRANNY  ENVELOPE  AND  OUTER 

PORTION  OF  THE  ENDOSPERM  OF  THE  GRAIN.    (X250.) 

P= pericarp,  consisting  of  (e)  epicarp,  (m)  mesocarp,  and  (d)  endocarp. 
£=endosperm,  consisting  of  (a)  layer  of  aleurone  cells  (rich  in  pro- 
tein, but  free  from  starch),  and  {/>)  parenchymatous  cells  (packed 
with  starch  grains) ;   (/)  testa;   («)  nucellus. 


>— £ 


parenchymatous  cells  of  the  endosperm,  and  to  this  end  the 
whole  of  the  complicated  machinery  of  modern  milling  is  con- 


WHEAT-FLOUR 


271 


trived.  In  practice,  however,  a  perfect  separation  is  never 
attained,  and  the  flour  always  contains  more  or  less  of  the  other 
portions  of  the  wheat  grain,  which  are  termed  the  "offal,"  con- 
sisting of  the  embryo  or  germ  and  the  bran  formed  of  the  pericarp 
and  the  integuments  and  outermost  layer  of  the  seed.  The  in- 
clusion of  this  offal  raises  the  mineral,  fat,  and  proteid  content. 
But  the  oil  in  the  germ  is  very  prone  to  develop  rancidity,  and 
it  is  principally  for  this  reason  that  it  is  rejected  in  modern 
milling.  "  Standard  "  flour  is  described  as  "  80  per  cent,  of  the 
wheat  with  all  the  germ  and  semolina,"  but  this  is  unsatisfac- 
tory for  more  than  one  reason.  In  the  first  place,  the  term 
"  semolina  "  does  not  connote  any  particular  part  of  the  grain; 
it  is  merely  a  trade  name  for  the  coarser  fragments  of  endosperm 
produced  in  the  break-roller  system,  and  is  therefore  incapable 
of  exact  definition.  In  the  second  place,  the  requirement  that 
the  flour  shall  contain  80  per  cent,  of  the  wheat  grain  is  by  no 
means  satisfactory  as  a  "  standard  "  of  quality  or  composition. 
Wheats  differ  considerably  from  one  another,  and  the  skin  or 
branny  envelope  bears  a  smaller  ratio  to  the  endosperm  in  the 
case  of  a  large  grain  than  of  a  small  grain. 

The  composition  of  ordinary  baker's  flour  and  of  "  whole- 
wheat "  flour  varies  with  different  samples,  but  the  following 
results  would  fairly  represent  the  average: 


Ordinary  Baker' 

"  Whole- Wheat 

Flour. 

Flour. 

(100 

parts 

by  weight.) 

Albuminoids  (N  = 

=  6-25)      . 

12-3 

13-8 

Carbohydrates 

71-2 

68-1 

Fat     . . 

1-3 

1-9 

Sugar . . 

1-3 

1-2 

Fibre  . . 

0-4 

1-7 

Ash     . . 

0-7 

1-4 

(P2O5) 

.     .      ..           (o-2i) 

(0-67) 

Moisture 

12-8 

II-9 

lOO-O 

lOO-O 

The  Analysis. 

Physical  Characters  of  Flour. — The  colour  should  be  white, 
and  the  flour  clean;  a  yellow  hue  denotes  age  or  fermentation, 
and  fermenting  flour  disarranges  the  digestive  system,  producing 
flatulence,  dyspepsia,  diarrhoea,  etc.  There  should  be  no  acid 
or  mouldy  odour,  and  no  taste  of  acidity  or  mustiness.     Taken  up 


272  LABORATORY   WORK 

in  the  lingers  the  flour  sliould  be  smooth  and  soft,  with  no 
lumpy  or  gritty  feel;  it  should  knit  or  bind  together,  and  a 
little  flecked  on  to  the  wall  should  mostly  adhere;  on  mixing 
with  a  little  water,  the  dough  should  draw  out  into  stringy 
masses. 

There  must  be  complete  freedt)m  from  fungi  and  other  parasitic 
growths.  If  flour  is  stored  in  a  damp  place,  the  number  of 
microbes  present  increases  rapidly,  and  poisonous  alkaloidal 
products  may  result  from  prolonged  storage  under  such  con- 
ditions. 

As  compared  with  other  flours,  wheat-flour  is  characterized 
by  the  large  amount  of  crude  gluten  it  contains ;  and  it  is  to  this 
substance — or  rather  to  one  of  its  constituents  termed  "  gliadin  " 
— that  the  peculiar  adhesiveness  of  the  flour,  which  makes  it 
so  peculiarly  adapted  for  bread-making,  is  due.  If  flour  is  made 
into  a  dough  with  water,  and  then  the  dough  is  thoroughly 
washed,  it  is  this  crude  gluten  which  remains  behind  as  a  sticky 
mass,  the  starch  and  soluble  substances  {i.e.,  sugar,  soluble 
albumin  and  salts)  being  washed  away.  It  is  of  great  value, 
therefore,  both  as  a  test  of  the  purity  and  also  of  the  quality 
of  the  flour,  to  estimate  the  amount  of  this  substance.  One 
means  of  effecting  this  is  the  following: 

Weigh  out  a  quantity  of  flour — say  50  grammes — place  it  in' 
a  small  basin,  and  carefully  mix  it  with  lukewarm  water  (about 
16°  C.)  into  the  condition  of  stiff  dough  ;  then  slowly  and 
thoroughly  work  up  the  dough  with  the  Angers,  either  under 
water,  or  while  allowing  a  gentle  stream  of  the  warm  water  to 
fall  upon  it.  As  the  dough  becomes  more  and  more  washed, 
the  water  which  is  being  constantly  emptied  away  and  renewed 
gets  clearer  and  clearer,  and  the  dough  more  stringy  and  sticky. 
Ultimately,  the  starch  and  all  the  soluble  materials  in  the  original 
flour  are  carried  away,  and  the  water  escapes  in  a  perfectly  clear 
condition.  Nothing  then  but  crude  gluten,  containing  generally 
a  fraction  over  i  per  cent,  of  fats  and  salts,  remains;  and  the 
entire  absence  of  starch  can  be  proved  by  treating  with  a  little 
iodine.  The  gluten  should  then  be  spread  out  in  a  tared 
(weighed)  flat-bottom  dish,  dried  at  105°  C,  and  finally 
weighed. 

A  more  exact  method  of  estimating  the  proteid  material  is 
as  follows: 


wheat-flour  273 

The  Estimation  of  Nitrogenous  Organic  Matter  in  Flour 
(Kjeldahl's  Process). 

Special  Reagents  required. — (i)  Decinormal  sulphuric  acid;  (2)  deci- 
normal  soda  solution;  (3)  methyl-orange  indicator;  (4)  strong  sodium 
hydrate  solution  (500  grammes  added  to  500  c.c.  distilled  water,  and  well 
boiled  to  free  from  ammonia) ;  (5)  strong  sulphuric  acid,  free  from  nitrates 
and  ammonium;   (6)  red  oxide  of  mercury;   (7)  potassium  sulphate. 

The  Process, 

1.  Weigh  from  0-5  to  3  grammes  of  the  material  (according 
to  its  richness  in  nitrogen),  and  transfer  to  a  strong  hard-glass 
boiling-flask. 

2.  Add  25  c.c.  of  strong  sulphuric  acid  and  075  gramme  of 
red  mercuric  oxide.  Support  the  flask  in  a  slanting  position  on 
a  tripod,  and  by  means  of  a  bunsen  burner  keep  the  acid  just 
below  its  boiling-point  for  half  an  hour.  As  fumes  of  sulphuric 
acid  will  escape  from  the  mouth  of  the  flask,  the  heating  must 
be  done  in  a  fume-cupboard. 

3.  If  at  the  end  of  half  an  hour  the  mixture  is  still  black, 
12  grammes  of  potassium  sulphate  (free  from  nitrates)  are  added. 
This  raises  the  boiling-point,  and  the  heating  is  continued  for 
a  few  minutes  after  the  liquid  is  clear  and  has  no  more  than  a 
faint  yellow  tint. 

4.  Let  cool;  add  about  500  c.c.  of  ammonia-free  water,  and 
be  careful  to  wash  thoroughly  the  mouth  and  neck  of  the  bottle 
with  this  water.  Then  more  than  neutralize  the  acid  by  means 
of  the  strong  soda  solution.  Also  add  about  20  c.c.  of  a  4  per 
cent,  solution  potassium  sulphide,  in  order  to  precipitate  all  the 
mercury  as  sulphide,  and  thus  prevent  the  formation  of  mercur- 
ammonium  compounds. 

5.  Distil  over  the  ammonia  into  50  c.c.  of  decinormal  sul- 
phuric acid,  using  a  condenser  with  a  bulb  ("  anti-splasher")  in 
the  condensing-tube  a  little  above  the  boiling-flask,  in  order  to 
guard  against  the  liquid  spurting  over. 

6.  When  about  250  c.c.  of  distillate  have  been  collected,  the 
acidity  is  titrated  with  the  decinormal  soda  solution,  using 
methyl-orange  as  indicator.  The  difference  between  the  amount 
of  soda  solution  required  to  neutralize  the  50  c.c.  of  decinormal 
acid,  before  and  after  the  addition  of  the  distillate,  represents 
the   ammonia  which  has   come   over.     Each  c.c.   of  the  acid 

18 


274  LABORATORY    WORK 

neutralized  by  the  ammonia  =0-0014  gramme  of  nitrogen,  and 
the  nitrogen  multiphed  by  the  factor  5-68  (as  the  protein  of 
wheat  contains  an  average  of  17-6  per  cent,  of  nitrogen)  repre- 
sents the  amount  of  albuminoid  or  proteid  mateiial  in  the 
amount  of  the  flour  examined. 

Notes  on  the  Process. — 'i  he  organic  matter  is  burnt  up  in  this 
process  by  moist  combustion,  and  the  resulting  ammonia  com- 
bines with  the  sulphuric  acid  to  form  ammonium  sulphate.  The 
addition  of  excess  of  soda  liberates  the  ammonia  from  the  acid 
and  enables  it  to  be  distilled  over.  It  is  necessary  to  perform  a 
blank  experiment  occasionally  in  order  to  test  the  reagents. 
The  figure  of  the  blank  experiment  (commonly  only  about 
0'2  c.c.  of  decinormal  alkali)  should,  of  course,  be  deducted  in 
arriving  at  the  total  nitrogen  obtained  from  the  material. 

Example. — Two  grammes  of  flour  furnished  ammonia  which 
neutralized  19-5  c.c.  of  the  decinormal  acid. 

.-.  there  are  19-5  x  0-0014=  0-0273  gramme  of  nitrogen  in 
2  grammes  of  flour=  1-365  grammes  of  nitrogen  in  100  grammes 
of  flour. 

.".  1-365  X  5-68  =  7-75  per  cent,  of  proteid  material,  or  approxi- 
mately 7-7  per  cent,  of  gluten. 

The  gluten  varies  from  8  to  12  per  cent.;  if  the  gluten  is 
less  than  8  per  cent,  the  flour  is  not  pure  wheat-flour;  and  if  it 
cannot  be  drawn  out  into  long  fine  threads  without  breaking  it 
is  poor  in  quality.  Rye  yields  a  plastic  gluten  which  cannot  be 
separated  by  washing. 

The  water  of  flour  should  not  exceed  18  per  cent,  by  weight, 
since  more  than  this,  besides  fraudulently  throwing  up  the  weight, 
impairs  its  keeping  power  by  favouring  the  development  of  fungi 
and  the  acetic  and  lactic  acid  fermentations,  which  may  some- 
times produce  gastro-intestinal  disturbance.  The  amount  of 
moisture  is,  of  course,  ascertained  by  drying  a  weighed  quantity 
of  flour  over  the  water-bath  (and  subsequently  in  the  hot-air 
oven),  the  loss  in  weight  being  due  to  moisture. 

The  ash  of  wheat  consists  chiefly  of  phosphates  of  potassium, 
magnesium  and  calcium,  and  small  quantities  only  of  salts  of 
silica,  sodium,  iron,  etc. ;  the  amount  should  not  much  exceed 
I  per  cent.,  and  as  much  as  2  per  cent,  would  imply  that  mineral 
adulterants  have  been  added.  In  making  the  estimation, 
cautiously  incinerate  a  weighed  quantity  of  dried  flour  in  a 
platinum  dish,  until  a  clean  white  ash  remains.     During  ignition 


WHEAT-FLOUR  275 

a  hard  mass  of  carbon  forms,  and  it  is  a  good  plan  to  moisten 
this  with  a  strong  solution  of  nitrate  of  ammonia,  then  dry  and 
continue  the  ignition.  It  may  be  necessary  to  repeat  this  treat- 
ment before  a  clean  ash  is  obtained. 

Adulteration. — Foreign  mineral  matter,  which  is  seldom  now 
added,  may  be  roughly  estimated  by  shaking  up  with  chloro- 
form, when  the  flour  floats  and  most  of  the  added  mineral 
matter  settles  at  the  bottom  of  the  vessel.  The  treatment  is 
repeated,  in  order  that  it  shall  be  as  inclusive  as  possible,  and 
the  sediment  collected,  dried  and  weighed;  it  can  also  be 
examined  as  to  its  nature. 

The  presence  of  any  added  mineral  matter  (calcium  phosphate, 
sulphate  and  carbonate,  etc.)  is  also  readily  detected  in  the  ash, 
as  this  is  found  to  be  exceptionally  high. 

Phosphates  and  other  "  improvers  "  are  employed  to  improve 
the  baking  quality  of  certain  flours  by  improving  the  quality 
of  the  gluten,  and  thus  increase  the  strength  and  water-absorbing 
capacity  of  the  flour. 

A  mixture  in  about  equal  proportions  of  acid  potassium  and 
magnesium  phosphates  and  flour  is  said  to  be  an  effective  im- 
prover. 

The  use  of  calcium  acid  phosphate  has  greatly  extended  in 
recent  years,  and  as  this  substance  may  contain  a  large  pro- 
portion of  calcium  sulphate,  which  is  valueless.  Dr.  Hamill,  in 
a  Report  to  the  Local  Government  Board  (1911),  recommends 
that  a  maximum  limit  of  10  per  cent,  of  calcium  sulphate  in 
calcium  acid  phosphate  should  be  fixed. 

There  is  no  evidence  that  these  phosphatic  improvers  increase 
the  organic  phosphorous  compounds  present ;  they  are  added  with 
the  object  of  increasing  the  amount  of  bread  which  can  be 
obtained  per  sack  of  flour. 

Rarely  it  is  by  the  addition  of  other  flours  and  meals  that 
sophistication  is  practised,  when,  of  course,  the  cheaper  varieties 
are  selected,  such  as  maize.  To  detect  rice-starch  in  wheat 
33'33  grammes  of  flour  are  made  into  a  ball  with  17  grammes  of 
water,  and  worked  between  the  fingers  in  a  fine  stream  of  water 
over  a  fine-meshed  sieve.  The  starch  and  waste  water  (thus 
separated)  are  well  shaken,  and  set  aside  for  twelve  hours  in  a 
large  conical  flask,  when  the  starch  separates  in  three  well- 
marked  layers  which  can  be  separated  by  decantation.  The 
top  layer  contains  most  of  the  small  starch  granules,  and  the 


27t)  LABORATORY   WORK 

bottom  layer  the  largest  grains,  whereas  the  middle  layer  is 
mainly  composed  of  the  cellulose  and  proteid  element  of  the 
flour.  .  When  rice-starch  is  present,  it  is  almost  entirely  deposited 
in  this  layer,  and  its  presence  can  be  detected  in  so  small  a  pro- 
portion as  I  per  cent.  (E.  Collin).  Maize  is  difficult  to  detect; 
but  if  the  flour  is  mixed  with  clove  oil  the  hilum  of  maize  appears 
under  the  microscope  as  a  black  star  or  spot.  This  is  not  the 
case  with  the  other  starches  most  commonly  used  to  adulterate 
flour. 

Old  flour  is  occasionally  passed  through  the;  mill  with  fresh 
flour;  in  these  cases  there  is  marked  acidity,  a  reduction  in  the 
fat  and  the  quality  of  the  gluten. 

The  degree  of  whiteness  of  flour  depends  upon  the  fineness  of 
the  grade,  and  to  some  extent  upon  the  variet}'  of  the  wheat; 
and  the  artificial  means  of  producing  a  white  flour  is  by  means 
of  bleaching  with  nitrogen  peroxide  gas  (NOg).  The  bleaching 
effect  appears  to  be  due  to  the  destruction  of  a  yellow  colouring 
matter  dissoh-ed  in  a  thin  layer  of  oil  which  surrounds  each 
granule  of  starch.  Dr.  Hamill,  reporting  upon  this  matter  to  the 
Local  Government  Board,  states  that  the  practice  cannot  be 
regarded  as  free  from  risk  to  the  consumer,  especially  when 
regard  is  had  to  the  inhibitory  effect  of  the  bleaching  agent  on 
digestive  processes.  This  bleaching  of  flour  is  prohibited  in 
Switzerland,  United  States,  and  certain  of  the  Australian  States. 
The  amount  of  nitrite  left  in  the  flour  is  extremeh-  minute,  and 
in  the  bread  made  from  the  flour  it  is  still  further  reduced;  and  for 
practical  purposes  it  may  be  presumed  that  when  over  1-5  parts 
of  nitrites  per  million  are  present,  the  flour  has  been  bleached. 
Small  amounts  of  nitrate  are  also  formed  as  a  result  of  bleaching. 
Extremely  small  quantities  of  nitrites  can  be  tested  by  the 
Ilosvay  method,  by  which  the  colour  produced  with  sulphanilic 
and  a-naphthylamine  hydrochloride  in  acetic  acid  solution  may 
be  compared  with  standards  containing  known  amounts  of 
sodium  nitrite. 

Dr.  MacFadden,  in  a  Report  to  the  Local  Government  Board, 
draws  attention  to  the  fact  that  the  relation  which  may  exist 
between  apparently  very  minute  alterations  in  the  nature  of 
staple  food  materials  and  the  production  of  great  and  far- 
reaching  changes  in  nutrition  has  been  strikingly  demonstrated 
in  recent  investigations  into  certain  obscure  disorders  of  metabol- 
ism, of  which  the  disease  known  as  beri-beri  may  be  taken  as  an 


WHEAT-FLOUR  277 

example,  and  the  time  has  arrived  for  taking  a  wider  view  than 
has  hitherto  been  customary  of  the  danger  to  healtli  wiiich  may 
arise  from  the  sophistication  of  foodstuffs. 

The  bleaching  of  flour  by  chemical  oxidizing  agents  has  been 
introduced  in  response  to  the  public  demand  for  a  white  loaf. 
A  simple  test  for  bleached  flour  is  to  shake  up  about  ^  ounce  of 
the  flour  with  2  fluid  ounces  of  petrol.  If  unbleached,  the  spirit 
takes  up  a  yellow  colour,  but  not  so  if  the  flour  has  been  bleached. 
The  bleaching  of  flour  by  means  of  nitrogen  peroxide  renders  the 
gluten  indigestible  (Hafliburton). 

The  seeds  of  the  darnel  grass,  or  Lolium  temulentum,  may 
gain  access  to  wheat  or  oat  flour;  they  are  said  to  possess  narcotic 
poisoning  properties.  Neither  the  starch  grains  nor  the  testa  are 
characteristic  under  the  micioscope,  since  both  resemble  oats 
very  closely;  but  the  addition  of  alcohol  causes  a  greenish 
colour  to  appear,  together  with  a  pecuhar  repulsive  taste,  if 
flour  contains  these  seeds. 

The  corn-cockle  {Agrostemma  githago)  consists  of  large,  dull 
black  seeds,  showing  small  protuberances.  They  are  markedly 
poisonous. 


CHAPTER  VI 


BREAD 


It  is  only  with  wlieaten  bread  that  the  following  chapter  deals. 

Among  the  means  for  obtaining  the  porosity  of  bread  is  in- 
cluded the  use  of  baking-powders.  These  consist  most  generally 
of  a  mixture  of  sodium  bicarbonate,  tartaric  acid  and  rice-flour. 
The  rice-flour  is  used  to  keep  the  powder  dry,  and  to  prevent 
chemical  action  setting  up  until  it  is  moistened. 

The  tartaric  acid  baking-powders  are  by  far  the  most  common, 
but  powders  are  also  sold  in  which  the  acid  constituent  is  fur- 
nished by  acid  phosphate,  and  in  other  cases  by  the  sulphuric 
acid  contained  in  some  form  of  alum  salt.  It  has  been  argued 
that  the  employment  of  acid  phosphates  is  of  value  as  replacing 
the  phosphates  lost  to  the  bread  by  the  removal  of  the  bran. 

Certainly  the  use  of  baking-powders  containing  alum  should  be 
condemned.  The  reaction  between  potassium-alum  and  sodium 
bicarbonate  has  been  shown  to  result  in  the  production  of  alu- 
minium hydrate,  and  the  hydrate  of  alumina  is  known  to  be  dis- 
solved (with  difficulty)  by  the  gastro-intestinal  juices.  Such  a 
baking-powder,  analyzed  by  the  writer,  gave  23  per  cent,  sodium 
bicarbonate,  33  per  cent,  alum,  and  44  per  cent,  ground  rice,  etc. 

Self-raising  flour  is  flour  containing  the  essential  elements  of 
baking-powder. 

In  the  process  of  cooking,  some  of  the  starch  of  the  wheat- 
flour  is  converted  into  maltose. 

The  composition  of  good  bread  (freed  from  moisture)  is  approxi- 
mately as  follows: 

Starch,  dextrin,  etc.         . .  . .  . .     82 "6 


Nitrogenous  matter 
Maltose 

Fat 

Salts 


II -4 
40 
0-6 

i;4 

loo-o 


278 


BREAD  279 

Physical  Characters.— The  bread  should  be  fairly  dry,  light 
and  spongy;  and  not  sodden,  acid,  or  musty.  It  should  be  clean 
and  of  a  good  colour — nearly  white,  that  is  to  say;  for  a  yellow 
or  dirty  colour  betrays  age  and  poorness  in  quality.  A  peculiar 
violet  tint  is  given  to  wheat  containing  melampyrum  and  other 
species  of  Scrophulariacea  and  trefolium  (trefoil) .  Other  growths 
sometimes  give  the  bread  a  dirty  blue  appearance  {rhinanthus, 
etc.) ;  agrosiemma  (corn-cockle)  furnishes  a  greenish  tint.  Oidium 
aurantiacum  has  caused  poisoning  in  France.  It  is  a  reddish- 
yellow  mould,  giving  a  bitter  taste  and  offensive  odour  to  the 
bread. 

The  estimation  of  water  and  mineral  matter  is  performed  as  in 
flour.  Fifty  grammes  of  crumbs  is  a  convenient  amount  to 
work  with. 

The  moisture  in  bread  should  not  much  exceed  40  per  cent,  in 
the  crumb  part  and  25  per  cent,  in  the  crust. 

The  Ash.— An  increase  in  weight  of  the  ash  of  bread  over  that 
of  the  original  flour  is  due  to  the  common  salt  and  the  baking- 
powder  which  are  added  in  the  process  of  baking.  But  any 
excess  of  ash  above  3  per  cent,  would  be  due  to  added  minerals 
(such  as  gypsum  and  chalk),  which  have  been  rarely  added  with 
the  object  of  improving  the  colour. 

As  chlorides  and  other  salts  may  be  volatilized  by  the  pro- 
longed ignition  necessary  to  furnish  a  white  ash,  the  ash  must 
be  procured  at  as  low  a  temperature  as  possible. 

To  estimate  the  silica,  treat  the  ash  first  with  strong  hydro- 
chloric acid,  then  with  a  little  distilled  water  and  boil;  next 
filter  through  a  Swedish  filter-paper,  wash  the  platinum  dish  by 
boiling  more  distilled  water  in  it,  and  filter  these  washings  also 
through  the  same  paper.  When  the  platinum  dish  is  perfectly 
clean,  well  wash  the  material  upon  the  filter-paper  with  small 
quantities  of  hot  distilled  water;  dry  in  the  water-oven,  and 
then  ignite  in  a  porcelain  crucible  with  lid;  finally  weigh  the 
ash;  deduct  the  weight  of  the  filter-paper  ash,  and  the  difference 
is  silica.     It  should  not  exceed  0-2  per  cent. 

To  estimate  acidity  soak  10  grammes  of  bread  in  about  50  c.c. 
of  water  for  one  hour,  filter,  and  titrate  the  filtrate  with  a  deci- 
normal  alkaline  solution,  using  phenolphthalein  as  indicator. 
The  number  of  c.c.  of  decinormal  soda  used  to  neutralize  the 
acidity  x  6  =  milligrammes  of  glacial  acetic  acid  in  10  grammes 
of  bread.    Express  results  in  terms  of  glacial  acetic  acid  per  cent. 


200 


LABORATORY   WORK    ^ 


Anything  over  o-i2  per  cent,  is  rather  acid,  and  tliis  figure 
should,  therefore,  not  be  exceeded. 

Adulteration. — Mashed  potatoes  are  looked  upon  as  a  legitimate 
addition  in  slight  amount  where  sponginess  is  dependent  upon 
fermentation,  since  they  favour  this  action.  It  has  been  said 
that  they  are  added  to  increase  the  weight  and  whiten  the 
loaf,  and  since  they  contain  between  70  and  80  per  cent,  of 
moisture,  they  help  to  keep  the  bread  moist;  but  generally 
only  the  strained  liquor  in  which  the  potatoes  have  been  cooked 
and  mashed  is  employed,  in  order  to  obtain  a  sweeter  loaf. 

Rice  when  added  also  serves  the  purpose  of  giving  a  good 
white  colour  to  the  loaf. 

Dr.  Alford  has  recorded  an  outbreak  of  lead-poisoning,  affect- 
ing from  fifteen  to  twenty  persons,  arising  from  the  consumption 
of  flour  which  had  been  ground  by  an  old  mill-stone  in  which 
large  spaces  had  been  filled  in  with  lead. 

The  starch  grains  of  the  flour  used  in  the  manufacture  of 
bread  become  so  altered  by  the  process  of  cooking  (on  account  of 
the  rupture  of  their  envelopes)  as  to  lose  most,  if  not  all,  of  their 
microscopic  characteristics. 

Fungi  may  be  discovered,  and  notably  the  different  forms  of 
penioilliwn  ("mildew");  these  may  create,  if  sufficiently 
numerous,  patches  of  greenish,  brownish,  or  reddish  discolora- 
tion. Oiduim  auranfiacum  furnishes  an  orange  hue.  These 
fungi  should  condemn  the  bread  off-hand,  for  they  may  give  rise 
to  considerable  gastro-intestinal  disturbance. 


FIG.    54. PENICILLIUM    GLAUCUM.       (x  ABOUT    200.) 

Alumina  exists  normally  in  pure  flour  as  the  silicate  of 
alumina;  but  it  has  been  added,  as  alum,  to  inferior  flour,  so  as 
to  check  the  fermentative  action  whereby  a  large  amount  of 
sugar  (glucose)  is  formed  and  a  discoloured  bread,  unpleasant 
to  the  palate,  results.  Alum  thus  improves  the  taste  and  colour 
of  the  bread,  and  also  to  some  extent  its  porosity. 


BREAD 


281 


The  whitening  of  flour  has  also  been  obtained  by  bleacliing 
methods,  so  that  the  eolour  is  no  certain  indication  of  quality. 

At  the  present  day,  largely  owing  to  the  adoption  of  other 
expedients,  alum  is  very  little  employed,  and  it  is  rare  that 
alumina  is  detected  in  amounts  which  denote  an  excess  over 
that  which  may  be  normally  present.  Large  quantities  of  the 
salt  were  formerly  added  to  flour,  and  the  great  decline  in  its 
use  commenced  with  the  passing  of  the  Sale  of  Food  and  Drugs 
Act,  1875.  It  was  generally  employed  in  quantities  of  about 
15  to  35  grains  to  a  4-pound  loaf,  but  more  than  100  grains  have 
been  separated. 

It  is  generally  held  in  this  country  that  no  addition  of  alum 
should  be  countenanced,  and  that  very  small  amounts  in  an 
article  such  as  bread,  of  which  large  quantities  are  consumed, 
may  prove  deleterious  to  health,  by  inducing  dyspepsia,  constipa- 
tion, etc.  There  is,  however,  some  conflict  of  opinion  as  to 
whether  small  quantities  of  alum  are  injurious  to  health;  but 
there  can  be  no  doubt  that  it  is  an  adulteration  under  the  Bread 
Acts  of  1822  and  1836. 

The  best  test  for  the  presence  of  alum,  and  one  which  will 
detect  as  little  as  i  grain  per  pound  in  bread  which  has  not 
undergone  acid  fermentation,  is  as  follows: 

Reagents  required. — i.  A  strong  freshly-made  tincture  of  logwood, 
prepared  by  digesting  5  grammes  of  freshly-cut  logwood  chips  in  100  c.c. 
of  strong  alcohol. 

2.  A  solution  of  ammonium  carbonate  (15  grammes  of  ammonium 
carbonate  in  100  c.c.  of  distilled  water). 

About  5  c.c.  of  each  of  these  reagents  are  added  to  about 
30  c.c.  of  water,  and  pieces  of  the  crumb  of  the  bread  are  cut 
from  the  loaf,  moistened  with  a  little  water  and  left  to  soak  in 
this  mixture  for  a  few  minutes ;  the  fluid  is  then  drained  off  and 
the  bread  gently  dried  over  the  water-bath.  The  presence  of 
alum  is  denoted  by  the  appearance  of  a  permanent  lavender  or 
violet  colour,  according  to  the  amount  present;  while  the  parts 
of  the  bread  which  contain  no  alum  are  first  stained  the  bright 
colour  of  the  logwood  solution,  and  afterwards  change  to  a  dirty 
brown  tint.  Wynter  Blyth  soaks  the  bread  paste  in  gelatine, 
and  then  tests  this  with  logwood  and  ammonium  carbonate;  a 
neater  reaction  is  thereby  obtained. 

The  operator  must  be  careful  that  he  is  not  led  astray  b^^ 
magnesium  salts,  which  are  capable  of  creating  a  lavender  tinge 


282  LABORATORY   WORK 

almost  identical  with  that  of  alum;  but  the  colour  created  by 
these  salts  is  certainly  not  so  permanent  upon  drying  as  that 
furnished  by  alum. 

In  order  to  avoid  the  effect  of  acidity  of  old  meal  or  of  sour 
bread  on  the  logwood  test,  the  following  method  is  recommended: 
From  10  to  20  grammes  of  the  bread  are  triturated  into  a  paste 
with  water,  some  sodium  chloride  (fiee  from  alkali)  added,  and 
then,  after  the  addition  of  10  drops  of  freshly  prepared  logwood 
tincture,  5  grammes  of  pure  potassium  carbonate  are  gradually 
mixed  in.  After  being  well  mixed,  the  whole  is  washed  with 
100  c.c.  of  water  in  a  beaker  and  allowed  to  settle.  In  a  few 
minutes  the  supernatant  liquid  becomes  a  greyish  to  a  deep 
blue  when  alum  is  present,  and  a  reddish-violet  tint  when  it  is 
absent. 

As  a  confirmatory  test  (Herz)  for  alum  in  flour,  10  grammes 
of  the  flour  are  mixed  with  water  and  allowed  to  stand  for 
ten  minutes;  filter,  concentrate,  and  precipitate  the  proteids 
with  tannic  acid  solution.  Filter  and  add  2  drops  of  tincture 
of  cochineal.  In  the  presence  of  alum  a  carmine  red  colour  is 
obtained. 

One  of  the  best  methods  of  separating  and  estimating  the 
alumina  in  bread  is  the  following: 


Quantitative  Estimation  of  Alum  (Dupre  and 
Wanklyn). 

(i)  Incinerate  |-  pound  of  flour  or  bread  to  a  grey  or  reddish 
ash. 

(2)  Separate  silica,  etc.,  by  treating  with  strong  HCl  and  then 
boiling  water;  filter;  wash  filter  with  boiling  w'ater.  The 
filtrate  contains  phosphates  of  calcium,  magnesium,  iron  and 
aluminium. 

(3)  Add  5  c.c.  of  ammonia  solution  (when  all  the  phosphates 
are  precipitated) ;  then  20  c.c.  of  strong  acetic  acid  are  added 
gradually  (which  redissolves  the  phosphates  of  calcium  and 
magnesium);  filter;  wash  filter  with  boiling  w-ater,  dry,  ignite, 
and  w^eigh.  The  residue  contains  the  iron  and  aluminium 
phosphates  and  the  filter-paper  ash. 

(4)  Dissolve  up  the  residue  in  strong  HCl  and  dilute  to  200  c.c, 
and  then  estimate  the  iron  colorimetrically  on  the  lines  indicated 
in  Water  Analysis. 


BREAD  283 

{5)  Convert  the  Fe  thus  estimated  into  ferric  phosphate  l)y 
multiplying  by  2-7,  and  deduct  this  amount  from  tlic  total  weiglit 
found  in  Step  (3) ;  further  deduct  the  weight  of  filter  ash,  and 
the  difference  is  aluminium  phosphate.  Convert  this  into 
crystallized  ammonium  alum  (the  commercial  "  alum  ")  by 
multiplying  by  37,  and  calculate  to  grains  per  pound. 

Conclusions  to  be  Drawn  from  the  Amount  Estimated. — If  the 
amount  of  alumina  represents  more  than  from  6  to  10  grains  of 
alum  per  4-pound  loaf,  in  the  vast  majority  of  cases  the  latter 
has  been  fraudulently  added;  some  pure  flours,  however,  may 
undoubtedly  contain  a  greater  quantity  than  this,  and  hence  it 
is  difficult  to  lay  down  any  definite  quantity  as  a  standard 
beyond  which  the  proof  of  fraudulent  addition  may  be  certainly 
established.  The  alumina  which  is  taken  up  from  the  soil  is  in 
the  form  of  silicate,  and  if  the  amount  of  alumina  considerably 
predominates  over  that  of  the  silica,  that  circumstance  would 
denote  the  presence  of  "  added  alum.." 


CHAPTER  VII 

THE  AVERAGE  COMPOSITION  OF  OTHER  FLOURS  AND  MEALS* 
—THE  MICROSCOPIC  CHARACTERS  OF  THE  DIFFERENT 
STARCH  GRANULES 


Oats. 

Arrowroc 

)T. 

Starch,   dextrin,   and 

ccllu- 

Starch,  dextrin,  and 

cellu- 

lose 

64-5 

lose 

83-0 

Nitrogenous  matter 

I2-0 

Nitrogenous   matter 

0-8 

Fat 

6-u 

Mineral  ash  .  . 

0'2 

Mineral  ash  . . 

3.0 

Water 

i6'0 

Sugar 

2'0 

Water 

12-5 
lOO'O 

Tapioca 

lOO'O 

Sago. 

Starch,  dextrin,   and 

cellu- 

Starch,    dextrin,    and 

cellu- 

lose 

S7-3 

lose 

S6-0 

Nitrogenous  matter 

0-6 

Nitrogenous  matter 

0-8 

Mineral  ash  .  . 

O'l 

Mineral  ash  .  . 

O'l 

I3-I 

Water 

Lentils 

I2-0 

Water 

1000 

lOO'O 

CORNFLOURf    (M 

Starch,  dextrin,   and 

lose 
Nitrogenous  matter 

Fat 

Mineral  ash  . . 
Water 

aize). 
cellu- 

68-5 

13-0 

3-5 

1-5 

13-5 

Starch,   dextrin,   and 

lose 
Nitrogenous  matter 

Fat 

Mineral  ash  .  . 
Water 

cellu- 

58-5 

25*0 

2'0 

2-5 

I2'0 

IQO'O 

lOO'O 

Pea. 

Bean  (Haricot). 

Starch,   dextrin,   and 

cellu- 

Starch,  dextrin,   and 

cellu- 

lose 

58-5 

lose 

57-5 

Nitrogenous  matter 

23-0 

Nitrogenous  matter 

23-5 

Fat 

2*0 

Fat 

2-0 

Mineral  ash  .  . 

2-5 

Mineral  ash  .  . 

3.0 

Water 

14-0 

Water 

14*0 

lOO'O 

lOO'O 

*  Chietiy  compiled  from  the  results  of  analyses  made  by  the  writer. 
t  Cornflour  consists  of  the  nearly  pure  starch  of  maize  or  rice. 

284 


THE 


E    AVERAGE    COMPOSITION    OF   FLOURS    AND    MEALS       285 


Rye. 

Starch,   dextrin,   and   cellu 

lose 
Nitrogenous  matter 

Fat 

Mineral  ash  .  . 

Sugar 

Water 


Potato. 
Starch,  dextrin,  and  cellu 

lose 
Nitrogenous  matter 

Fat 

Mineral  ash  .  . 
Water 


68-0 

II'O 

2*o 

1-5 

3-5 

I4'0 

lOO'O 


22-0 
2-0 
O'l 
I-O 

74-9 

lOO'O 


Barley. 

Starch,   dextrin,   and   cellu- 
lose 
Nitrogenous  matter 

Fat 

Mineral  ash  .  . 
Water 


yi'O 

"•5 

1-5 

I'O 

15-0 

lOO'O 


Rice. 
Starch,   dextrin,   and   cellu- 
lose           .  .          - .          •  ■  7'^'5 
Nitrogenous  matter             .  .  6-5 

Fat 0-5 

Mineral  ash  .  .          .  .          •  •  0-5 

Water            14-0 


A  silicate  of  magnesia  (talc)  is 
sometimes  employed  to  polish  or 
"  face  "  rice,  in  order  to  improve 
its  appearance;  oil  may  be  em- 
ployed to  increase  translucency ; 
and  blue  pigments  (ultramarine)  to 
improve  the  white  colour. 

The  more  expensive  of  these  flours,  or  meals,  are  liable  to  be 
adulterated  with  the  cheaper  kinds,  such  as  rice,  tapioca,  potato, 
and  maize. 

It  will  be  seen  that,  in  comparison  with  wheat,  barley  is  poor 
in  nitrogenous  matter  and  sugar,  but  rich  in  cellulose  and  mineral 
matter;  that  oats  are  exceptionally  rich  in  cellulose  and  fat, 
possess  a  high  amount  of  mineral  matter,  but  are  relatively  poor 
in  starch;  that  maize  possesses  a  high  amount  of  fat,  but  the 
cellulose  is  low;  that  rye  is  exceptionally  rich  in  sugar,  and  in 
other  respects  closely  approximates  to  wheat;  and  that  rice  is 
rich  in  starch,  but  poor  in  everything  else. 

The  amount  of  starch  in  any  substance  is  estimated  as  follows : 
Five  grammes  of  the  dried  and  powdered  material  are  mixed  with 
200  c.c.  of  4  per  cent.  HCl,  a  reflux  condenser  is  attached  to  the 
flask,  and  the  liquid  is  boiled  for  five  hours.  The  contents  are 
then  cooled,  made  slightly  alkaline  with  sodic  hydrate,  and  the 
dextrose  estimated  by  Fehling's  method.  The  dextrose  xo-g^ 
starch.  If  cellulose  is  present,  a  little  of  this  would  also  be  con- 
verted into  sugar  by  boiling  with  the  acid,  but  this  small  quantity 
is  often  ignored. 


286  LABORATORY  WORK 

The  Microscopic  Characters  of  the  Different  Starch 

Granules. 

The  starch,  of  which  the  foregoing  foodstuffs  are  mainly  com- 
posed, exists  in  the  form  of  microscopic  granules,  which  are  more 
or  less  characteristic  of  the  particular  plant  from  which  they  are 
derived,  on  account  of  their  difference  in  size,  shape  and  mark- 
ings. These  microscopic  granules  consist  of  an  extremely  thin 
envelope  of  cellulose  enclosing  the  starch  (granulose),  and  the 
latter  appears  to  be  generally  arranged  in  fine  superimposed 
strata — -which  accounts  for  the  "  stride,"  or  concentric  lines, 
commonly  discernible  upon  the  external  surface  of  the  granule. 

When  a  sample  of  any  flour  or  meal  is  to  be  examined  under 
the  microscope,  very  small  amoimts  are  placed  upon  several 
clean  glass  slides,  a  drop  of  water  is  applied  to  each  slide  and 
a  clean  cover-glass  is  pressed  firmly  down  over  the  powder  and 
water  to  evenly  distribute  the  powder.  It  is  impossible  to  get 
too  thin  a  layer  of  the  substance  in  order  that  a  satisfactor\' 
examination  may  be  made,  as  otherwise  granules  get  super- 
imposed and  conglomerated,  and  their  contours  and  markings 
cannot  be  defined.  It  is  a  good  plan,  therefore,  to  drop  a  small 
amount  of  the  powder  upon  the  slide,  and  then  to  gently  blow 
it  almost  all  away  again,  before  applying  the  water  and  cover- 
glass. 

It  is  important  that  the  reader  should  recognize  that  in  the 
description  which  follows  the  most  characteristic  features  are 
described.  It  must  not  be  thought  that  in  a  sample  of  arrow- 
root, for  instance,  each  granule  will  possess  the  characters 
described  under  that  head.  Such  is  by  no  means  the  case,  for 
some  may  have  the  hilum  in  the  centre,  or  even  at  the  small 
extremity  of  the  granule  (as  in  potato),  and  yet  the  sample  may 
be  pure;  but  many  of  the  granules  will  possess,  in  a  more  or 
less  marked  degree,  the  characters  described.  Where,  therefore, 
the  starch  grains  of  different  food-plants  somewhat  closely 
resemble  each  other  it  is  difficult  to  decide  as  to  whether  there 
may  be  some  slight  admixture,  although  considerable  adultera- 
tion admits  of  no  questioning;  but  when  these  grains  are  dis- 
similar in  appearance,  the  faintest  possible  amount  of  admixture 
is  readily  detected.  When  it  is  required  to  estimate  the  amount 
of  adulteration,  a  rough  percentage  of  the  foreign  starch  grains 
present  may  be  made  by  counting  them  upon  the  microscopic 


PLATE  V. 


ARROWROOT 


PEA  BEAN 

STARCH    GRANULES.     (X    250.) 

It.  C.  Boiis_field, photo. 


PLATE   VI 


\ 

1,  ■• 

-= 

) 

^ 

■;•' .'--' 

-  ■■    '  ' 

_) 

M 

£. 

-  ■'■; 

,,/-.? 


■  •  yv-  ■. 


_    ■-> 


-  ^^  -O  ^ 

MAIZE  TAPIOCA 

STARCH    GRANULES.      (X    250.) 

E.  C.  Bousjield,  photo. 


MICROSCOPIC    CHARACTERS    OF    FLOURS    AND    MEALS      287 

"  field  "  of  several  mounted  specimens.  When  the  percentage 
amount  of  foreign  starch  has  been  estimated,  a  careful  and 
thorough  mixture  is  made  up  containing  the  supposed  amounts 
of  the  ingredients  in  the  composition  under  examination;  this 
is  then  examined  under  the  microscope  and  the  counts  compared 
with  those  of  the  original  powder,  in  order  to  see  if  the  estima- 
tion which  has  been  made  is  broadly  correct.  If  not,  known 
quantities  of  the  pure  substance  are  mixed  with  fresh  quantities 
of  the  adulterants  found  until  a  microscopic  examination  shows 
that  the  approximately  true  percentages  have  been  arrived  at. 
In  cases  where  the  foreign  starch  granules  are  very  distinctive, 
the  number  in  the  specimen  may  be  counted  upon  a  plan  very 
similar  to  that  adopted  in  the  case  of  counts  of  blood-corpuscles. 

It  will  be  seen  that,  in  many  cases,  the  differences  between 
the  starch  granules  are  very  slight,  and  therefore  some  skiU  is 
requisite  in  detecting  them;  such  skill  is  only  acquired  from 
practice,  and  the  student  is  recommended  to  fit  up  a  small  case 
containing  samples  of  all  the  more  common  starches  and  to 
practise  assiduously  with  these.  Specimens  mounted  in  glycerine 
are  well  preserved  for  a  short  time.  A  J-inch  power  should  be 
employed,  and  this  suffices  for  all  practical  pui  poses. 

Mention  may  be  made  of  the  useful  adjunct  which  the  polari- 
scope  may  furnish  to  such  investigations.  For  polariscopic 
examination  glycerine  or  oil  should  be  used  instead  of  water. 
Starches,  such  as  potato,  arrowroot,  bean,  and  maize,  polarize 
well;  while  wheat,  rice  and  oatmeal  polarize  feebly. 

I.  Large  round  or  oval  granules,  more  or  less  flattened,  and 
showing  no  marked  concentric  "  strice  "  {or  at  most  only  a  feio  at 
the  margins),  together  with  other  granules  extremely  small  and  ill- 
defined. 

May  he  wheat,  barley,  or  rye. 

Wheat. — Relatively  few  "  intermediary  "*  sizes,  although  the 
larger  granules  themselves  vary  somewhat  in  size.  (A  linear 
hilum  and  strise  are  visible  under  a  very  high  power,  and  the 
small  granules  are  seen  to  be  angular.) 

Barley. — Similar;  but  the  large  granules  are  rather  more 
irregular  in  shape  and  somewhat  smaller,  and  "  intermediary  " 
sizes  are  more  commonly  present;  lumpy  forms  rather  more 
common. 

*  A  term  used,  in  this  connection,  to  denote  a  size  about  midway  hetween 
that  of  the  large  and  small  granules. 


288  LABORATORY   WORK 

Rye. — Similar;  but  many  show  a  rayed  hilum,  and  present 
cracked  edges;  the  granules  are  somewhat  larger,  and  more 
generally  circular  and  flattened  than  those  of  wheat  or  barley. 
Striations  often  distinct.  Rye-flour  is  darker  and  less  finely  ground 
than  wheat-flour. 

2.  Large  pyriform  or  oval  granules,  with  well-marked  concentric 
stricB  and  a  circular  or  short  linear  hilum. 

May  he  potato  or  arroicroot. 

Potato. — Typically,  a  well-marked  circular  or  stellate  hilum 
is  at  the  smaller  ex<-remity,  and  the  striae  aie  well  marked.  The 
granules  vary  considerably  in  size. 

Arrowroot. — Similar,  but  the  hilum  is  geneially  at  the  larger 
extremity,  and  the  granules  average  a  trifle  smaller  (with  the 
exception  of  the  arrowroot  named  "  tous-les-mois,"  in  which 
commonly  the  gianules  are  even  larger  than  those  of  potato, 
though  they  vary  considerably  in  size) .  The  granules  do  not  swell 
with  potassic  hydrate  solution,  as  do  those  of  potato,  and  the 


FIG.    55. BRUCHUS    PISI    (OF    THE    PEA,    BEAN,    ETC.).      (X  ABOUT    4O.) 

concentric  rings  are,  generally  speaking,  less  visible.  There  are 
many  varieties  of  arrowroot,  all  of  which  present  similar  general 
characteristics  as  to  their  starch  granules:  the  common  variety 
is  derived  from  Maranta  arundinacea. 

3.  Oval  or  reniform  granules,  with  faint  concentric  stricB,  a 
central  linear  hilum,  and  very  uniform  in  size. 

May  be  pea  or  bean. 

Pea. — Most  have  a  central  longitudinal  hilum,  which  presents 
a  puckered  appearance.     The  granules  are  large. 

Bean. — Similar;  but  somewhat  larger  and  more  flattened  {i.e., 
broader),  and  slightly  more  uniform  in  size.  The  hilum  is  much 
more  commonly  crossed  by  transverse  hues  ("  puckered  "). 

4.  Very  small  angular  and  faceted*  granules,  without  concentric 
stria. 

May  be  rice,  oatmeal,  or  maize. 

jlice. — The  minute  granules  tend  to  collect  into  angular 
masses. 

*  These  facets  are  due  to  the  close  juxtaposition  of  the  granules. 


MICROSCOPIC    CHARACTERS    OF    FLOURS    AND    MEALS      289 

Oatmeal. — The  granules  tend  to  collect  into  rounded  masses, 
and  are  slightly  larger  than  in  rice,  but  still  very  minute. 

Maize. — The  granules  are  much  larger  and  are  more  irregular 
in  shape,  which  tends  towards  the  circular;  they  possess  a  visible 
hilum  which  is  generally  stellate. 

5.  Irregular  in  size,  rounded,  or  partly  angular  with  rounded 
edges,  possessing  (generally)  a  central  hilum,  and  occasionally 
showing  ill-defined  concentric  stricB. 

May  be  sago  or  tapioca. 

Sago. — Mostly  large  and  irregular  in  shape;  many  elongated, 
with  one  larger  end  rounded  and  the  other  truncated.  Hilum 
stellate  or  linear. 

Tapioca.- — -Similar;  but  much  smaller,  and  many  granules  have 
a  tendency  to  be  truncated  by  one  facet.  Hilum  generally  more 
towards  the  rounded  extremity. 


FIG.    56. SECTION    OF   WHEAT    GRAIN    (oUTER    COAT)  .       (X50.) 

a,  Girdle  cells;  b,  cerealin  cells. 


In  order  to  get  rid  of  starch,  oleo-resin,  etc.,  and  thus  bring 
together  within  a  small  compass  much  of  the  vessels,  fibres,  and 
parenchyma,  the  following  steps  are  serviceable : 

Five  grammes  of  powdered  material  are  mixed  with  50  c.c.  of 
water  to  which  2  c.c.  of  HCl  (S.G.  i-i6)  are  added.  The  mixture 
is  boiled  for  ten  minutes,  and  then  centrifugalized ;  the  solid 
matter  is  washed,  partially  dried,  stirred  with  a  few  c.c.'s  of 
chloral  hydrate  solution ;  and  the  mixture  is  again  centrifugalized 
and  the  deposit  examined  under  the  microscope. 

The  flours  and  meals  from  cereals  also  give  evidence  under  the 
microscope  of  the  thin  envelope  of  the  grain,  called  the  skin  or 
testa ;  and  this  is  the  case  with  even  the  finest  ground  and  purest 
flours. 

19 


290 


LABORATORY   WORK 


In  wheat  the  envelope  is  composed  of  three*  fine  membranes, 
the  external  and  the  middle  both  consisting  of  flattened  cells, 
which  are  more  or  less  dovetailed  into  each  other. 

The  long  axes  of  the  cells  in  the  middle  coat  are  disposed  at 
right  angles  to  those  in  the  external,  the  latter  being  arranged 
with  their  long  axes  corresponding  with  that  of  the  grain. 

Unicellular  cells  with  pointed  apices  ("  hairs  ")  come  off  in 
tufts  from  the  external  coat  at  one  extremity  of  the  grain;  these 
"  hairs  "  are  simplj^  prolongations  of  the  cells. 

The  internal  coat  is  made  up  of  irregularly  rounded,  opaque- 
looking  cells,  which  frequentl}^  contain  one  or  more  oil  globules. 
The  starch  gi-anulcs,  comprising  almost  the  whole  of  the  interior 
of  the  grain,  are  included  within  a  thick-walled  cellular  network. 


FIG.       57. WHEAT.       TISSUE       FROM 

THE  "  TESTA  "  OF  THE  GRAIN, 
SHOWING  THE  APPEARANCE  OF 
THE  CELLS  FORMING  ITS  OUTER 
AND   INNER  MEMBRANES.    (X  lOO.) 


.^m^ 


FIG.  58. — BARLEY.  TISSUE  FROM 
THE  "  TESTA  "  OF  THE  GRAIN, 
SHOWING  THE  APPEARANCE  OF 
THE  CELLS  FORMING  ITS  OUTER 
AND   INNER  MEMBRANES,    (x  TOO.) 


In  barley  the  envelopes  are  the  same  as  those  in  wheat,  except 
in  the  following  respects : 

The  cells  forming  the  external  coat  are  shorter  and  more 
uniform  in  size  than  in  wheat,  and  their  outline  is  serrated 
instead  of  beaded;  they  carry,  moreover,  short  thick  hairs.  The 
cells  of  the  middle  coat  are  more  elongated,  and  those  of  the 
inner  coat  are  somewhat  smaller. 

Slight  as  these  differences  are,  it  is  to  the  envelopes  rather 
than  to  the  starch  granules  that  one  must  turn  in  order  to  dis- 
criminate between  wheat  and  barley. 

In  rye  the  testa  so  closely  resembles  that  of  wheat  that  it  is 
difficult  to  hit  upon  a  point  in  which  they  differ,  and  it  is  for- 
tunate that  the  starch  grains  afford  a  ready  means  of  distinguish- 
ing between  the  two. 

*  There  are  probably  six  in  all  under  very  high  powers. 


MICROSCOPIC   CHARACTERS    OF    FLOURS    AND    MEALS      2(Jl 

It  maybe  pointed  out  that  the  unicellular  hairs  are  somewhat 
shorter  than  in  wheat. 

In  maize  (Indian  corn)  the  envelopes  arc  two  in  number;  the 
external  consists  of  several  superimposed  layers  of  flattened, 
elongated  cells,  and  the  internal  of  a  layer  of  cells  of  irregular 
size  and  shape,  but  otherwise  resembling  the  internal  layer  of 
wheat.  A  very  characteristic  circumstance  about  maize  is  that 
the  cellular  network  which  holds  the  starch  granules  in  this 
plant  forms  an  irregular  mosaic,  most  often  pentagonal  but 
occasionally  polygonal  in  design. 

Spoilt  maize  taken  as  food  may  be  responsible  for  pellagra, 
which  is  probably  a  food  intoxication  induced  by  some  toxi- 
cogenic  saprophyte.  Many  varieties  of  parasite  are  found  on 
maize,  including  certain  moulds,  the  spores  of  which  are  not 
destroyed  by  cooking. 


FIG.     59. RYE.       TISSUE    FROM    THE 

"  TESTA  "  OF  THE  GRAIN,  SHOW- 
ING THE  APPEARANCE  OF  THE 
CELLS  WHICH  FORM  ITS  OUTER 
AND   INNER  MEMBRANES,    (x  lOO.) 


FIG.    60. OATS.       TISSUE    FROM    THE 

"  TESTA  "  OF  THE  GRAIN,  SHOW- 
ING THE  APPEARANCE  OF  THE 
CELLS  WHICH  FORM  ITS  OUTER 
AND   INNER  MEMBRANES,    (x  100.) 


In  oats  the  envelopes  consist  of  an  external  one  of  long  narrow 
cells  with  evenly  serrated  contours  (not  wavy  or  beaded),  and 
carr3nng  sharp  spinous  "hairs";  a  middle,  somewhat  similar 
coat,  but  indistinct  and  poorly  seen;  and  an  inner  layer  of 
cells  resembling  the  internal  one  of  wheat,  but  larger. 

In  rice  the  external  coat  of  the  husk,  consisting  of  long  narrow 
cells,  is  characterized  by  the  number  of  fine  silicious  particles 
it  contains,  which  are  collected  together  into  ridges  crossing 
each  other  at  right  angles.  The  spinous  hairs  are  long  and 
numerous,  and  the  other  coats,  of  which  there  are  several,  consist 
also  of  elongated,  narrow,  flattened  cells,  variously  arranged. 

The  "  polishings  "  from  white  rice  appear  to  contain  a  sub- 
stance the  absence  of  which  may  lead  to  beri-beri  when  white  rice 
is  the  staple  food. 


292  LABORATORY   WORK 

The  polishing  of  rice  results  in  the  removal  of  the  pericarp 
and  of  the  whole  of  the  greater  part  of  the  sub-pericarpal  layers 
of  the  rice  grain.  C.  Funk  has  pointed  out  that  a  satisfactory 
measure  of  the  degree  of  polishing  to  which  rice  has  been  sub- 
jected is  the  estimation  of  its  total  phosphorus,  and  that  a  rice 
which  jdelds  less  than  0-4  per  cent,  of  P2O5  cannot  safely  be 
permitted  to  form  the  staple  diet  of  man. 


CHAPTER  VIII 

MEAT— PARASITES  OF  FLESH— POISONING  BY  FOOD- 
MEAT  PREPARATIONS 

It  is  sometimes  necessary  to  make  a  laboratory  examination  of 
meat,  in  order  to  decide  whether  it  is  fit  for  human  consumption. 


The  Characters  of  Good  Meat, 

It  should  have  a  marbled  appearance,  due  to  little  streaks  of 
fat  between  the  muscular  fasciculi;  the  whole  surface  should 
have  a  glossy  appearance,  and  the  colour  should  be  of  a  bright 
florid  hue  and  not  too  dark,  or  the  meat  is  that  of  an  old  or 
diseased  animal.  The  colour  of  veal,  mutton  and  pork  is  always 
paler  than  that  of  beef,  and  this  fact  depends  to  some  extent 
upon  natural  causes  (the  flesh  of  all  young  animals  is  naturally 
paler  than  that  of  older  ones),  but  mostly  upon  the  fact  that 
calves,  sheep  and  pigs  are  bled  more  at  the  time  of  killing.  In 
old  animals  the  flesh  is  darker  and  tougher,  and  the  fat  more 
yellow  and  soft. 

The  connective  tissues  should  glisten  when  exposed,  and  the 
muscular  fasciculi  should  not  be  too  large  and  coarse. 

To  the  touch  the  meat  should  be  firm  and  slightl}^  elastic, 
which  implies  that  the  meat  is  fresh  and  has  set  well  (rigor 
mortis) ;  it  should,  moreover,  be  so  dry  upon  the  surface  that 
the  finger  is  only  slightly  moistened  by  being  passed  over  it; 
such  moisture  should  be  of  a  clear  red  colour  and  of  an  acid 
reaction.  In  taking  the  reaction  the  litmus-paper  should  first 
be  dipped  in  water,  as  otherwise  the  serum  glazes  the  paper  and 
obscures  the  reaction.  On  cutting  through  the  flesh,  the  whole 
thickness  should  present  a  uniform  colour,  or  the  interior  must 
be  but  very  slightly  paler  than  the  more  external  flesh. 

The  odour  of  meat  is  best  obtained  either  by  drenching  it 

293 


294  LABORATORY   WORK 

(when  finely  minced)  with  very  hot  water,  or  by  phmging  a  clean 
odourless  knife  or  new  wooden  skewer  deep  down  into  its  sub- 
stance— prefcrabl}^  in  the  direction  of  bone — and  then  with- 
dra\ving  and  smelling  the  knife.  The  peculiar  odour  of  good 
fresh  meat  is  familiar  to  all,  both  in  the  raw  and  cooked  state, 
and  any  departure  from  this  would  create  suspicion. 

The  fat  should  have  a  firm  and  greasy  feel;  the  normal  faint 
yellow  colour  must  not  be  excessive,  although  the  fat  of  animals 
fed  upon  some  oil-cakes  acquires  a  very  marked  yellow  hue. 
The  fat  deepens  in  colour  with  age.  It  should  present  no 
hemorrhagic  points. 

Any  lymphatic  glands  attached  should  be  firm,  smooth,  slightly 
moist,  and  of  a  pale,  greyish-brown  appearance  on  section. 

The  pleura  and  peritoneum  should  be  smooth,  glistening  and 
transparent. 

The  marrow  of  the  bones  should  be  light  red;  that  from  the 
bones  of  the  hind-quarters  sets  firmly  within  twenty-four  hours, 
but  that  from  the  fore-quarters  remains  diffluent  for  a  longer 
period. 

The  ash  of  the  meat  is  alkaline,  and  consists  almost  entirely 
of  phosphates  and  chlorides. 

The  Characters  of  Bad  Meat. 

Bad  flesh  is  frequently  moist,  sodden,  flabby  and  dropsical, 
and  may  be  infected  with  parasites.  It  must  be  remembered, 
however,  that  the  flesh  of  young  animals  is  always  pale  and 
moist. 

Some  parts  of  the  meat  may  feel  softer  than  others — that  is 
to  say,  there  is  not  a  uniform  resistance  to  pressure,  and 
occasionally  there  may  be  emphysematous  crackling.  The  flesh 
of  \eal  and  lamb  may  be  blown  out  artificially  and  the  surface 
then  smeared  with  fat,  and  thus  an  artificial  plumpness  is  given 
to  poor  meat.  Dishonest  butchers  may  also  rub  melted  fat 
over  the  flesh  of  diseased  animals  to  give  it  a  healthy  and  glossy 
appearance. 

The  fat  is  generally  soft  and  flabby,  or  gelatinous ;  frequently 
highly  coloured,  or  exhibiting  small  hasmorrhagic  points. 

Any  attached  lymphatic  glands  may  be  enlarged,  softened, 
hypencmic,  ecchymosed,  caseated,  calcified  or  suppurated.  The 
marrow  of  the  bones  is  discoloured  (brownish)  and  sets  badly. 


MEAT  295 

A  deep  purple  or  dark  tint  suggests  that  the  ;i,ninial  has  not 
been  killed  and  bled,  but  has  died  with  the  blood  in  it,  and 
probably  of  some  acute  feverish  condition  or  pulmonary  com- 
plaint.    A  yellow  or  mahogany  hue  denotes  bile-stained  flesh. 

Should  the  meat  be  very  pale  ("  white  flesh  "),  and  the  animal 
an  adult  one,  fatty  infiltration  or  degeneration,  or  fibroid  infiltra- 
tion, may  be  the  cause.  A  magenta  hue  of  the  flesh  points  to 
some  acute  specific  condition  being  present  at  the  time  of  death. 
Well-defined  and  dark-coloured  areas  full  of  blood  are  due  to 
hypostatic  congestion  or  post-mortem  staining. 

Pus  may  be  seen  lying  between  the  muscle  fibres,  and  boils  or 
small  abscesses  may  be  present  (as  in  anthrax,  etc.). 

There  is  frequently  too  great  a  proportion  of  bone  to  flesh, 
the  animal  having  been  greatly  emaciated.  The  reaction  of  the 
juice  (which  may  be  dark  or  discoloured)  may  be  alkaline  or 
neutral. 

The  odour  may  be  that  of  putrefaction  or  of  a  faint  and 
sickly  nature.  The  pleura  and  peritoneum  may  be  wet  or 
roughened,  opaque,  congested,  or  blood-stained. 

Sometimes  there  is  an  odour  of  physic,  as  when,  previous  to 
death,  odorous  and  volatile  drugs  (such  as  camphor,  prussic  acid, 
turpentine,  creosote,  chloroform,  etc.)  have  been  administered; 
or  the  animal  may  have  fed  upon  odorous  plants;  or,  subse- 
quent to  death,  the  carcass  may  have  been  hung  in  an  atmo- 
sphere which  is  odorous  from  any  cause  (tobacco,  carbolic  acid, 
etc.). 

It  has  been  shown  that  no  dangers  to  the  meat  would  arise 
from  the  administration  during  life  of  medicaments  such  as 
arsenic,  antimony  (tartar  emetic),  or  strychnine.  The  animal 
may  in  some  cases  take  in  poison  by  its  food,  by  feeding  upon 
such  herbs  as  bryony,  meadow-saffron,  rhus  toxicodendron,  etc. 

There  are  few  changes  which  are  so  easy  to  detect  as  commencing 
putrefaction  in  fish ;  this  is  fortunate,  inasmuch  as  decomposition 
sets  in  rapidly  and  appears  to  be  more  generally  productive  of 
poisonous  symptoms  than  decomposing  meat.  The  bright  gills, 
the  prominent  eyes,  the  elastic  resistance  of  the  firmly  adherent 
flesh,  and  the  absence  of  any  but  the  characteristic  odour,  are 
all  evidence  of  freshness.  The  soft  inelastic  feel,  the  readiness 
with  which  the  flesh  can  be  detached  from  the  bone,  and  the 
stale  and  unpleasant  odour,  furnish  the  chief  clues — and  the 
most    reliable — of    commencing    decomposition.     It    has    been 


296  LABORATORY   WORK 

found  possible  to  revive  the  greyish  gills  by  artificial  colouring 
agents,  and  to  keep  the  eyes  prominent  by  a  small  piece  of 
stick,  fixed  trans\ersely  in  the  head,  so  that  it  presses  the  eye 
outwards  on  either  side. 

Greenness,  iridescence,  and  sometimes  luminosity,  may  be 
seen  upon  the  surface  of  the  flesh  of  decomposing  fish.  Stale 
fish  float,  while  fresh  fish  sink  in  water. 

In  putrefaction  of  meat  the  flesh  softens,  and  tears  readily; 
it  becomes  paler ;  the  elastic  resistance  gradually  diminishes  and 
becomes  less  uniform — i.e.,  some  parts  are  softer  than  others; 
the  characteristic  odour  is  developed;  the  marrow  softens  and 
turns  brownish;  and  the  juices  become  alkaline  in  reaction,  due 
to  ammonia  and  substituted  ammonias  being  formed  by  the 
action  of  schizomycetes.  Later,  the  meat  becomes  of  a  greenish 
hue,  and  a  glance  then  suffices  to  detect  the  presence  of  putre- 
faction. Occasionally  meat  becomes  luminous,  chiefly  from  the 
presence  of  Bacillus  phosphorescefis  ;  but  putrefaction  eventually 
disperses  this  condition.  Putrid  meat  may  grow  dull,  dark 
moulds  upon  its  surface. 

As  a  test  of  putrefaction  Eber  recommends  the  use  of  a  reagent 
composed  of  i  part  of  hydrochloric  acid,  3  parts  of  alcohol  and 
I  part  of  ether.  A  few  c.c.  of  this  reagent  are  placed  in  a  cylinder, 
which  is  then  shaken  so  that  the  reagent  applies  itself  to  the 
inner  surface  of  the  cylinder.  If  a  fragment  of  meat  in  the  state 
of  incipient  putrefaction  is  introduced  on  the  end  of  a  wire,  greyish 
or  whitish  fumes  of  ammonium  chloride  will  generally  appear. 

The  moulds  which  grow  on  the  surface  of  meat  are  of  numerous 
varieties — penicillium,  mucor,  phycomyces,  verticillimii,  oospora, 
etc.  Red  growths  of  Bacillus  prodigiosus  may  also  be  associated 
with  mould.  There  is  little  or  no  evidence  that  these  growths 
or  their  products  are  injurious  to  health,  although  the  meat  is 
rendered  unsightly  and  often  unsaleable.  Mould  contain ination 
is  especially  liable  to  occur  when  meat  has  been  improperly 
handled  or  stored. 

Certain  diseases  may  cause  characteristic  appearances  in  the 
meat.  When  any  such  suspicion  attaches  itself  to  the  sample  of 
meat  under  examination,  it  is  a  great  advantage  to  obtain  a  glance 
at  the  offal  of  the  animal,  and  more  especially  to  carefully  inspect 
the  liver,  lungs  and  l3miphatics.  The  term  "  offal  "  includes  the 
head,  the  feet,  the  skin,  and  all  internal  organs  except  the  kidney; 
the  remainder  of  the  animal  is  termed  the  "  carcass." 


PARASITES    OF    FLESH 


297 


It  is  when  there  is  evidence  of  parasitic  attack  that  the  flesh 
presents  the  most  characteristic  appearances. 

Of  those  organisms,  which  are  commonly  classified  as  "  animal 
parasites  of  flesh,"  some  only  are  capable  of  infecting  human 
beings  when  the  flesh  is  eaten. 


Harmless  Animal  Parasites  of  Flesh. 

Coccidia  oviformes  (Leuckart)  infest  most  animals  (rarely  man), 
and  are  chiefly  found  in  the  livers  of  rabbits,  where  they  appear 
as  small  white  nodules,  which  under  the  microscope  are  seen  to 
contain  clear  ovoid  bodies  with  either  granular  contents  or  egg- 
like structures  known  as  sporoblasts.  Ccenufus  cerebralis  forms 
hydatids,  varying  in  size  from  a  pea  to  a  small  walnut,  in  the 
brain  and  spinal  cord  of  the  ox  and  sheep.    It  is  the  cystic  worm 


FIG.   61. COCCIDIUM  OVIFORME,   SHOWING   DEVELOPMENT  OF  SPOROBLASTS. 


of  TcBfiia  ccenurus  of  the  dog.  Cysticercus  fisiformis  is  found  in 
the  abdominal  cavity  and  liver  of  the  rabbit  and  hare;  it  is 
occasionally  found  in  man,  and  the  cysts  are  about  the  size  of  a 
pea.  C.  tenuicollis  is  found  in  the  abdominal  cavity  of  animals 
generally;  it  is  the  hydatid  of  the  tape-worm,  T.  marginata, 
which  inhabits  the  intestine  of  the  dog;  the  cysts  vary  in  size 
from  a  pea  to  a  small  orange,  and  do  not  invade  the  organs; 
the  long  thin  neck  is  characteristic  of  the  parasite.  C.  serialis 
is  the  immature  form  of  a  tape-worm  affecting  dogs;  the  cysts, 
varying  in  size  from  a  hazel-nut  to  a  pigeon's  egg,  are  found 
Under  the  skin  and  between  the  muscles.  Strongylus  filaria  in 
the  bronchial  tubes  of  sheep,  5.  micrurus  in  the  lungs  of  cattle, 
and  S.  paradoxicus  in  the  lungs  of  the  pig,  are  nematodes.  There 
is  another  parasite  found  in  the  lungs  of  sheep,  known  as  Strongy- 
lus riifescens,  of  which  the  eggs  or  embryos  are  deposited  in  the 
lung  substance,  forming  little  nodules  which  are  usually  of  a 
greyish-yellow  colour.    This  condition  is  found  in  adult  animals. 


298  LABORATORY   WORK 

and  is  \-ory  common;  it  is  called  by  many  "pseudo-tubercu- 
losis "  of  sheep.  The  lungs  of  at  least  60  per  cent,  of  all  sheep 
slaughtered  are  affected  by  this  parasite. 

Certain  nodular  masses  in  frozen  quarters  of  meat  arriving 
from  Australia  have  been  found  to  contain  the  parasitic  worm 
Onchocerca  Gibsoni,  which  gives  rise  to  a  condition  known  as 
onchocerciasis. 

Dr.  Leiper  found  no  evidence  of  vitality  in  the  worm  or  in  its 
embryo  in  the  Australian  beef  arriving  in  this  country,  and  it 
seems  to  be  impossible  for  the  parasite  to  develop  in  man  from 
eating  the  affected  meat.  Apart,  however,  from  this  danger,  the 
meat  itself  should  be  classed  as  unsound.  The  condition  is 
most  marked  in  the  fore-quarters,  where  it  is  more  or  less  con- 
fined to  the  region  of  the  flank  and  brisket. 

Dangerous  Anim.^l  Parasites  of  Flesh. 

Cysticerci. — The  cysticerci,  or  "  bladder- worms,"  cause  the 
condition  known  as  "  measles  "  in  the  pig,  ox  and  sheep.  Cysti- 
cerci celhdoscB  are  the  bladder-worms  which  form  a  stage  in  the 
development  of  Tcenia  solium.  In  the  flesh  of  the  pig,  and  rarely 
in  that  of  dogs,  monkeys,  or  man,  a  number  of  small  oval  or 
round  cysts  are  seen,  occupying  a  position  between  the  muscle 
fibres,  and  commonly  of  the  size  of  a  small  pea — though  they 
have  been  found  as  small  as  -^-^  inch,  and  as  large  as  ^  inch,  in 
length.  They  are  surrounded  by  a  pale,  milky-looking  fluid,  and 
the  cyst  wall  shows  a  white  spot  (generally  central)  upon  its 
surface.  The  affected  flesh  is  pale,  soft,  unduly  moist  and  flabby, 
and  has  a  smooth,  slippery  feel.  The  flesh  does  not  set  well,  and 
quickly  decomposes.  Sometimes  there  is  some  degree  of  calci- 
fication of  the  capsule,  and  the  result  is  that  when  sections  are  cut 
a  grating  sensation  is  experienced. 

The  bladders  should  be  incised  with  a  sharp  knife,  and  the 
worm  examined  by  a  powerful  hand-lens,  when  at  one  extremity 
will  be  found  the  blunt  square  head  provided  with  a  sucker  at 
each  "  angle,"  and  a  fringe  of  about  twenty-eight  booklets 
placed  more  centrally.  These  latter  are  very  characteristic, 
and  must  always  be  found  before  a  definite  diagnosis  is  ventured 
upon. 

Those  cysts  that  are  dried  up  and  indistinct  can  be  made 
visible  by  soaking  in  weak  acetic  acid.     Ostertag  attaches  great 


PARASITES   OF   FLESH 


299 


diagnostic  importance  to  the  rounded  or  oval  calcareous  cor- 
puscles which  are  so  generally  embedded  in  the  tissue  of  the  head, 
but  which  disappear  on  the  addition  of  acetic  acid.  The  liver 
and  the  muscles  of  the  shoulders,  intercostals  and  loins,  are 
chiefly  affected. 

A  staining  test  will  generally  suffice  to  determine  if  the  cysti- 
cerci  are  alive  or  dead.  If  dead,  the  whole  bladder- worm 
readily  stains  with  carmine ;  if  alive,  the  head  at  least  resists  the 
stain. 

Cysticercus  bovis,  or  "  beef -measles,"  chiefly  affects  the  calf, 
and  is  never  found  in  man.  It  is  somewhat  smaller  than  C.  cellu- 
loses, and  possesses  a  flat  head  with  no  booklets,  but  merely 
suckers,  around  which  there  is  frequently  a  considerable  deposit 
of  pigment;  and  on  the  surface  of  the  head  there  is  a  pit-like 


FIG.    62. HEAD    OF   T^NIA 

SOLIUM.     (OBJ.  I  INCH.) 


FIG.    63. HEAD    OF    TJENIA    MEDIO- 

CANELLATA.       (OBJ.  -|-  INCH.) 


depression  ("  frontal  suction  cup  ").  It  develops  into  the  adult 
tape-worm  called  Tcsnia  mediocanellata,  or  T.  saginata,  which  is 
longer  than  T.  solium. 

Fish  are  subject  to  parasitic  attack,  and  notably  is  this  the 
case  with  the  cod,  in  which  many  parasites  have  been  found. 
Cooking  effectually  destroys  them,  for  in  the  case  of  fish  the  flesh 
is  not  palatable  unless  the  cooking  is  thorough. 

Bothriocephalus  latus,  a  tape -worm  which  is  almost  limited  to 
certain  parts  of  the  continent  of  Europe,  is  even  larger  than 
Tcania  mediocanellata,  and  has  a  club-shaped  head,  not  armed 
with  rostellum  or  booklets,  but  possessing  two  deeply  grooved 
longitudinal  suckers,  one  on  each  side.  The  eggs  are  oval  and 
comparatively  large,  with  a  characteristic  operculum.  Man  is 
infected  through  eating  imperfectly  cooked  fish,  especially  the 
pike,  perch,  and  several  members  of  the  salmon  family.  There  is 
no  cysticercus  form. 


300 


LABORATORY   WORK 


T.  cchinococcHs  is  the  small  tape-worm,  of  three  or  four  seg- 
ments, which  is  commonly  found  in  the  dog.  The  encysted 
stage  ("  hydatids")  is  most  generally  found  in  the  lungs  and 
liver,  of  oxen,  sheep  and  swine,  but  also  (more  especially  in 
Iceland)  in  man.  The  hydatids  consist  of  thin  pale  vesicles, 
floating  in  a  clear  liquid,  and  the  whole  is  encysted  in  a  tough 
capsule.  The  inner  lining  of  the  capsule  consists  of  ciliated 
epithelium,  and  inside  of  the  cyst  wall  there  are  generally  many 
so-called  "  brood  capsules"  (Fig.  64).  The  cysts  vary  in  size 
from  a  pin's  head  to  that  of  a  large  orange.  They  may  exist  in 
such  numbers  in  the  liver  that  they  replace  the  greater  part  of  the 
entire  tissue  of  that  organ. 

The  condition  is  diagnosed  with  certainty  by  the  microscope, 
either  by  the  discovery  of  the  characteristic  heads  or  detached 


FIG.  64. BROOD  CAPSULE  OF  AN  ECHINOCOCCUS. 


hooklets  in  the  clear  liquid  of  the  cyst;  valuable  corroborative 
evidence  being  furnished  by  the  fact  that  the  liquid  is  quite 
free  from  albumin,  and,  in  consequence,  does  not  coagulate  on 
boiling. 

Tcsnia  nana  is  the  smallest  human  tape-worm  (12  to  20  milli- 
metres in  length),  and  is  not  uncommon  in  Italy.  The  head  con- 
tains four  suckers,  and  a  rostellum  carrying  twenty-two  to 
twenty-four  hooklets.  It  differs  from  T.  solium  in  being  very 
much  smaller,  and  the  rostellum  of  the  latter  carries  a  double 
row  of  hooklets,  twenty-eight  in  number. 

T.  cucumerina  is  a  little  larger  than  T.  nana  ;  it  occurs  in  man, 
especially  in  Norway  and  Sweden,  but  it  is  most  common  in  the 
dog.  The  head  contains  four  suckers,  and  three  or  four  rows  of 
hooklets  (sixty  in  all)  are  disposed  round  the  rostellum. 

Among  the  Cestoda  monstrosities  may  sometimes  be  observed, 
with  abnormalities  as  to  the  number  of  suckers  and  hooklets. 


PARASITES    OF   FLESH 


^,01 


Trichina  spiralis. — This  parasite  has  been  fonnd  in  tJic  flesh 
of  many  different  animals  (pigs,  pigeons,  eels,  etc.),  but  most 
commonly  by  far  in  that  of  pigs;  oxen  and  sheep  do  not  suffer 
from  attack  by  these  nematodes.  The  disease  is  often  seen  in 
Germany,  but  rarely  in  England. 

The  shape  of  the  minute  worms  is  nearly  that  of  a  typical 
nematode — i.e.,  a  slender  rounded  body  tapers  gradually  at 
either  end;  the  extremity  which  constitutes  the  head  goes  to  a 
long  slender  point,  which  presents  a  small  central  orifice,  the 
mouth.  The  other  extremity,  the  tail,  ends  more  bluntly.  The 
worm  possesses  a  distinct  alimentary  canal,  and  even  rudimentary 
sexual  organs  are  present.  In  the  female  a  uterus  is  discernil)]e, 
which  will  frequently  be  seen  to  be  full  of  minute  free  embryos 


FIG.    65. TRICHINA    SPIRALIS,    ENCYSTED    IN    MUSCLE, 

(X  ABOUT    50    DIAMETERS.) 


curved  upon  themselves;  these  latter  have  been  observed  to 
become  extruded  from  the  vagina,  and  subsequently  to  move 
sluggishly  about  the  field  of  the  microscope.  The  male  worm  is 
much  smaller  than  the  female,  and  is  only  about  yV  ™ch  long 
when  mature;  the  length  of  the  latter  reaches  |  inch.  The  long 
slender  head  and  blunt  tail  are  two  characteristics  which  serve  to 
distinguish  these  worms  from  parasites  which  otherwise  resemble 
them,  such  as  Drac^mctdus  and  Filaria  sanguinis  hominis. 

The  small  worms  are  mostly  coiled  up  in  cysts,  so  disposed 
that  their  longest  diameter  is  in  a  line  with  the  muscular  fibres, 
and  a  drop  of  acid  will  stimulate  them  to  transient  movements 
if  they  are  alive.  These  cysts  lie  between  the  muscle  fibrillse, 
and  their  walls  are  sometimes  partially  or  completely  calcified. 
so  as  to  give  a  grating  sensation  when  the  finger  is  passed  over 


302  LABORATORY    WORK 

a  section  of  the  flesh.  This  calcareous  deposit  serves  to  shield 
the  parasites  from  the  destructive  consequences  of  salting,  and 
maybe  even  of  cooking.  There  may  be  from  one  to  three 
trichinae  in  a  cyst.  Frequently  25  per  cent,  of  these  parasites 
are  thus  encysted  in  the  diaphragm,  and  therefore,  when  possible, 
a  piece  of  this  muscle  should  be  procured ;  the  back  muscles,  on 
the  other  hand,  are  the  least  attacked. 

Either  a  section  may  be  made  of  the  muscle,  or  it  may  be  teased 
out  with  needles ;  and  in  the  case  of  a  long  muscle,  a  point  near 
its  insertion  should  be  selected,  since  this  is  a  favourite  site  for 
encystment.  The  affected  muscle  is  seen  to  be  pale  and  oedema- 
tous,  and  if  the  worms  are  encapsuled,  small,  rounded  (or  more 
truly,  lemon-shaped),  whitish  specks,  averaging  about  the  size 
of  a  very  small  pin's  head,  are  visible  to  the  naked  eye.  These 
can  be  made  very  distinct  by  means  of  a  hand-lens;  but  a  low 
power  of  the  microscope  should  be  employed  in  every  case,  when 
the  most  characteristic  appearance  will  be  got  by  making  a  thin 
longitudinal  section  of  the  affected  muscle  and  immersing  this  in 
potassic  hydrate  solution  of  medium  strength,  which  serves  to 
make  the  muscle  fibres  transparent  and  leaves  the  worm  exposed 
in  its  coiled  condition  within  the  capsule.  The  soaking  should 
not  be  prolonged  beyond  a  minute  or  two,  or  the  worm  itself  will 
also  be  cleared  up.  Glycerine  is  a  good  mounting  medium  when 
a  permanent  specimen  is  desired.  Sometimes  a  view  of  the  worm 
is  obscured  owing  to  considerable  calcareous  deposit  in  and 
around  the  walls  of  the  capsule;  in  these  cases  a  drop  of  dilute 
hydrochloric  acid,  run  under  the  cover-glass,  will  dissolve  up  the 
deposit;  or  an  oil  globule,  or  several,  may  partially  obscure  the 
worm,  when  a  drop  of  ether,  applied  in  a  similar  manner  to  the 
acid,  will  clear  away  the  fat.  There  are  generally  oil  globules 
at  the  poles  of  the  capsule. 

The  parts  which  are  most  likely  to  be  affected  will  easily  be 
remembered  if  it  is  borne  in  mind  that  the  worms  migrate  to 
their  settlements  from  the  gastro-intestinal  tract,  and  chiefly 
from  the  commencement  of  the  small  intestine.  The  diaphragm, 
the  liver,  the  intercostal  and  abdominal  muscles,  are  necessarily 
the  first  encountered,  and  therefore  suffer  most;  but  in  later 
stages  of  the  infection  there  is  scarcely  a  muscle  which  may  not 
be  affected. 

Ihere  are  small,  semi-transparent  bodies  called  "  psoro- 
spermia,"   or  "  Rainey's  capsules,"   which  to  the  naked  eye 


PARASITES   OF    FLESH  303 

resemble  trichinae ;  but  they  consist  of  small  dark  oval  or  elliptical 
bodies,  of  greater  length  than  encysted  trichinae.  They  are, 
moreover,  made  up  of  a  thick  membrane  formed  by  small  hair- 
like fibres  arranged  in  lines,  which  encloses  small,  kidney-shaped, 
granular  cells  closely  adherent  together;  and  the  whole  lies 
embedded  in  the  muscle  substance  itself— ^'.g.,  the  sarcolemma. 
They  are  extremely  common,  and  may  exist  in  the  flesh  of  most  of 
the  animals  used  for  human  consumption,  and  apparently  when 
eaten  they  produce  no  ill-effects. 

Several  other  obscure  bodies,  the  nature  and  significance  of 
which  we  are  still  more  ignorant  of,  may  exist  in  flesh,  such  as 
bodies  somewhat  resembling  pus  cells,  and  others  forming  minute 
concretions   or   tiny   hard   nodules.     Interesting   as   these   are 


FIG.    66. ONE    OF   RAINEY'S    CAPSULES.       (X4O.) 

pathologically,  they  are  rare ;  and  when  present,  even  in  numbers, 
do  not  appear  to  effect  the  wholesomeness  of  the  meat  to  any 
degree. 

Actinomyces. — The  "  ray  fungus  "  (actinomyces),  one  of  the 
"  fission  fungi,"  is  now  recognized  as  a  parasite  of  commoner 
occurrence  in  the  ox  than  was  once  suspected;  the  difficulties 
which  stood  in  the  way  of  an  earlier  appreciation  of  this  fact 
arose  from  the  circumstance  that  both  the  ante-  and  post-mortem 
appearances  of  actinomycosis  so  closely  simulate  those  of  tuber- 
culosis. 

It  has  not  yet  been  proved  that  the  disease  can  be  communi- 
cated by  the  flesh  of  animals  (bovines)  suffering  from  attack,  and 
the  vitality  of  the  fungus  when  exposed  to  heat  is  very  low. 

The  parasite  almost  entirely  affects  the  tongue,  the  jaws 
(especially  the  lower  one),  the  muscles  of  the  cheek  and  the 
lungs,  where  they  may  be  detected  by  the  naked  eye  as  small 
dirty  white  specks,  commonly  about  the  size  of  a  barley  grain, 
but  varying  from  the  tiniest  speck  to  |  inch  in  diameter.  On 
section,  the  centre  of  the  nodule  is  seen  to  be  softer  and  of  a 


304  LABORATORY    WORK 

greenish-yellow  colour,  or,  less  frequently,  the  nodule  is  firm  and 
fibrous  throughout.  The  condition  is  generally  associated  with 
considerable  fibrous  proliferation  of  affected  parts.  The  parasites 
assume,  when  encysted,  a  peculiar  synmietrical  appearance,  due 
to  the  fact  that  they  consist  of  small  linear  elements,  thicker 
at  one  extremity  than  at  the  other,  and  are  so  arranged  that  their 
smaller  extremities  are  all  directed  towards  a  central  point ;  the 
stellate  or  rayed  appearance  thus  created  is  sometimes  remarkably 
regular  and  uniform.  The  tongue  when  affected  is  hard  and 
swollen,  and  presents  the  flattened  nodules  chiefly  upon  its  dorsal 
aspect.  The  size  of  these  nodules  may  vary  from  I  inch  to 
2  inches,  and  the  glands  at  the  root  of  the  tongue  are  also  commonly 
infected. 

Distoma  Iwpaticmn. — To  examine  for  these  parasitic  trema- 
todes,  the  liver  should  be  taken  and  the  bile  ducts  carefully 


FIG.    67. DISTOMA    HEPATICUM.       (NATURAL    SIZE.) 

exposed.  In  shape  like  little  soles,  they  are  of  a  pale-brown  or 
slaty  colour,  and  are  provided  at  their  broad  extremity  with  two 
suckers,  one  at  the  anterior  end  and  the  other  a  little  above  the 
junction  of  the  anterior  and  middle  thirds  of  the  median  line. 
Their  surfaces  are  beset  with  many  little  warty  points,  and  they 
average  in  size  from  i  to  i|  inches  in  length  and  about  \  inch 
in  width.  The  bile  ducts  of  the  affected  liver  stand  out  on  the 
surface  ("  pipey  "  liver).  They  are  sometimes  found  encysted 
in  the  lungs  of  both  sheep  and  cattle,  when  the  cyst  wall  is 
usually  calcareous  and  contains  a  chocolate-coloured  fluid. 

Frozen  Meat. — Meat  which  has  been  frozen  may  be  detected 
by  expressing  a  drop  of  the  meat-juice  on  to  a  glass  slide,  covering 
with  a  cover-glass,  and  examining  by  the  microscope.  The  blood- 
corpuscles  will  be  found  to  be  much  distorted  in  form,  to  have  lost 
their  pigment,  and  to  be  floating  in  a  highly  coloured  serum; 
whereas  the  juice  of  fresh  meat  will  show  corpuscles  of  normal 
shape  and  colour,  floating  in  a  practically  colourless  serum. 


POISONING   BY   FOOD  30^ 

Compared  with  fresh  meat  frozen  meat  has  usually  a  darker 
and  more  diffused  red  colour  when  thawed,  owing  to  the  haemo- 
globin permeating  the  tissues;  it  is  also  somewhat  softer. 


Poisoning  by  Food. 

There  is  no  doubt  that  flesh  in  a  very  early  stage  of  decompo- 
sition disagrees  with  many  persons;  and  abundant  evidence  is 
'  not  lacking  that  when  an  advanced  state  of  putrefaction  has  been 
reached,  violent  gastro-intestinal  irritation,  followed  by  diarrhoea, 
vomiting  and  toxic  symptoms,  may  be  induced. 

Recorded  cases  of  grave  and  fatal  food  poisoning  have  been 
very  numerous,  and  minor  disturbances  of  the  gastro-intestinal 
tract  are  probably  often  due  to  small  doses  of  poisons  produced 
by  bacteria.  Often  the  offending  substance  appears,  to  all 
physical  tests,  to  be  quite  good  and  wholesome ;  but  the  meat  or 
jelly  formed  is  sometimes  observed  to  be  softer  and  moister,  and 
a  slight  peculiar  odour  has  been  noted.  The  poisonous  food  has 
most  commonly  been  brawn,  sausages,  ham,  pork,  veal  pie,  rabbit 
pie,  potted  shrimps,  tinned  salmon,  mackerel,  mussels  and  oysters ; 
but  many  other  varieties  of  food  have  been  incriminated,  such  as 
cheese,  ice-cream,  canned  goods,  potatoes,  etc.  There  is  a  strange 
absence  of  recorded  instances  where  the  flesh  of  sheep  has  been 
the  offending  food ;  but  this  is  seldom  used  in  the  preparation  of 
made  foods. 

In  food  which  has  become  poisonous,  a  living  micro-organism 
has  produced  an  organic  chemical  poison,  which  may  be  a 
ptomaine,  albumose  or  toxine.  The  substance  is  the  immediate 
cause  of  the  morbid  symptoms,  and  is  probably  produced  by  the 
action  of  the  micro-organisms  on  the  albuminous  constituents  of 
food.  Both  the  products  of  specific  micro-organisms  in  an  in- 
fected food  and  those  basic  substances  resulting  from  putre- 
factive micro-organisms  ("  ptomaines  ")  may  be  fleeting,  as 
regard  their  existence,  since  the  micro-organism  may  be  killed 
by  its  own  products  or  by  heat,  or  the  chemical  poison  (from  its 
unstable  nature)  may  undergo  decomposition ;  so  that  an  infected 
food  which  may  be  poisonous  at  one  time  may  fail  to  be  poisonous 
at  another.  The  micro-organisms  may  produce  their  peculiar 
chemical  poisons  from  material  affording  them  nourishment, 
which  may  be  either  outside  the  body  of  man  or  within  it.     Food 


3o6  LaBoratorV  Work 

poisoning  outbreaks  are  far  more  prevalent  in  the  summer 
months. 

In  the  majority  of  cases  the  symptoms  of  poisoning  occur 
within  twelve  hours,  when  they  are  due  to  the  ingestion  of  already 
formed  poisons  ("  intoxication  ") ;  but  in  other  cases  the  symp- 
toms may  be  delayed  for  twelve  to  forty -eight  hours,  when  they  are 
probably  due  to  a  food  "  infection  "  by  organisms  which  produce 
poisons  after  the  food  is  taken  into  the  human  body.  Generally 
there  is  a  mixture  of  bacilli  and  toxines  and  therefore  variable 
incubation  periods.  In  most  cases  the  sjmiptoms  include  con- 
siderable abdominal  pain  and  tenderness,  vomiting  and  diarrhoea, 
with  tenesmus,  headache,  and  marked  depression  or  collapse. 
Other  frequent  symptoms  include  dilated  pupils,  rashes,  and 
albuminuria.  The  temperature  may  be  raised,  but  in  most 
cases  it  is  subnormal.  Although  the  acute  symptoms  disappear 
after  two  or  three  days,  marked  prostration  may  persist  for  a 
much  longer  period. 

The  mortality  among  those  affected  by  meat  poisoning  is  often 
from  2  to  5  per  cent.,  and  except  in  cases  where  rapidly  fatal  results 
follow,  a  post-mortem  examination  usually  discloses  gastro- 
enteritis, and  sometimes  ulcers  in  the  small  and  large  intestines, 
with  enlarged  spleen  and  congested  liver  and  kidneys. 

The  most  frequent  fonn  of  meat  poisoning  results  from  con- 
suming the  flesh  of  diseased  animals,  and  is  associated  with  the 
presence  of  Bacillus  enieritidis  (Gaertner)  and  the  Paratyphoid 
Bacillus  ;  but  healthy  carcases  may  be  infected  in  the  slaughter- 
house by  the  knives  used  for  the  purpose  of  dressing  many 
animals,  and  cooked  or  uncooked  meat  may  be  infected  by  rats, 
mice,  flies,  dust,  ice,  or  the  soiled  hands  of  human  "carriers." 
Ptomaine  poisoning  from  eating  putrefied  meat,  and  usually 
associated  with  the  presence  of  B.  proteus  and  B.  coli,  is  less 
common;  and  "  botulismus,"  which  results  from  the  toxine  of 
B.  hotulinus,  is  of  extreme  rarity  in  this  country. 

Ptomaine  poisoning  has  most  frequently  resulted  from  eating 
meat  in  a  cut-up  condition  (sausages,  minced  meat,  etc.),  and 
game;  and  especially  meat  which  has  been  insufficiently  cooked 
(for  the  thorough  cooking  of  meat  destroys  B.  proteus  and  its 
toxines). 

Ptomaines  are  not  the  cause  of  extensive  outbreaks  of  meat 
poisoning.  The  infection  of  food  by  the  bacilli  of  the  Gaertner 
group  is  the  common  cause  of  these.     B.  suipestifer,  foimd  in 


POISONING   BY    FOOD  307 

the  pig's  intestine,  is  another  member  of  the  Gaertner  group, 
and  is  the  bacillus  of  swine  fever.  This  organism  has  been 
shown  to  be  responsible  for  some  outbreaks  of  poisoning  follow- 
ing the  consumption  of  pig's  flesh. 

The  power  of  certain  shellfish  to  create  violent  gastro-intestinal 
disturbance  and  urticaria  is  well  recognized;  mussels,  cockles 
and  oysters  collected  from  near  sewage  outfalls  have  had  virulent 
poisonous  properties  ascribed  to  them,  and  they  may  convey  the 
infection  of  enteric  fever.  From  mussels  a  poisonous  ptomaine, 
mytilotoxine,  has  been  isolated  by  Brieger.  This  exists  chiefly 
in  the  hepatic  organ  of  the  mussel.  Acute  gastro-intestinal  and 
profound  nervous  symptoms  may  follow  the  consumption  of 
either  the  raw  or  cooked  mussel.  Perch,  sturgeon,  turbot,  pike, 
crabs,  shrimps,  salmon  and  sardines  have  all  given  rise  to  poison- 
ing, either  from  the  development  of  putrefaction  toxines,  or  from 
bacterial  infection  or  intoxication.  Some  fish  normally  contain 
a  toxine  poisonous  to  man,  others  develop  such  a  poison  only  in 
the  spawning  season.  The  consumption  of  canned  fish  may  give 
rise  to  symptoms  akin  to  "  botulismus." 

Some  ptomaines  are  highly  poisonous,  while  many  are  inert. 
The  majority  of  the  known  ptomaines  contain  only  C,  H  and  N, 
and  represent  simple  ammonia  substitution  compounds.  The 
kind  of  ptomaine  formed  will  depend  upon  the  organism  present, 
the  nature  of  the  food  substance,  the  temperature,  the  stage  of 
putrefaction,  etc. 

A  large  number  of  toxic  bodies  have  been  isolated  and  de- 
scribed, some  of  the  more  important  being — 


Methylguanidine 

Dihydrocollidine 

Neurine 

Choline 

Muscarine 


Poisonous. 
Poisonous. 
Poisonous. 
Poisonous. 

Poisonous.      Obtained  from  poison- 
ous mushrooms  and  fish. 

Gadinene But  little  poisonous.     Obtained  from 

putrid  fish. 
Mytilotoxine        . .  . .     Poisonous.     Obtained  from  mussels, 

taken    from    positions    liable    to 
sewage  pollution. 
Tyrotoxicon         ..  ..     Poisonous.     Obtained   from   cheese, 

cream,  and  ice-creams. 


308  LABORATORY   WORK 

The  B.  botulinus  is  an  anaerobic  organism,  and  botulism 
generally  results  from  the  eating  of  sausages  in  thick  skins 
(German  sausages)  and  other  food  which  has  been  hermetically 
stored  or  embedded  in  fat. 

In  botulismus  the  main  symptoms  are  not  gastro-intestinal, 
but  nervous,  such  as  dryness  of  mouth  and  throat,  difficulty  in 
swallowing,  ptosis,  double  vision,  convulsive  muscular  tremors, 
vertigo,  constipation,  retention  of  urine,  disturbances  of  heart's 
action  and  of  respiration;  consciousness  is  unimpaired,  and 
the  combined  symptoms,  which  generally  appear  in  from  twenty- 
four  to  thirty-six  hours,  though  sometimes  earlier,  are  akin  to 
those  of  atropine  poisoning  (Dieudonne). 

Vanilla  flavouring  in  sauces  or  ice-cream  has  often  given  rise, 
within  two  hours,  to  vomiting,  tenesmus,  diarrhoea,  and  signs  of 
collapse.  The  explanation  appears  to  be  that  the  vanillin,  by 
its  reducing  action,  favom^s  the  growth  of  anaerobic  bacteria ;  the 
vanilla  itself  being  harmless. 

Potatoes  may  give  rise  to  similar  symptoms  of  poisoning,  which 
are  said  to  be  due  in  some  cases  to  a  considerable  increase  of  the 
trace  of  the  poisonous  substance  "  solanin  "  to  be  found  in  normal 
potatoes,  but  generally  to  bacterial  decomposition  by  proteus 
bacilli  (Dieudonne).  It  has  been  recommended  that  in  order  to 
guard  against  solanin  poisoning,  the  peel  and  any  sprouts  should 
always  be  thoroughly  removed. 

Cheese,  milk,  cream,  butter,  and  ice-creams,  etc.,  may  all 
rarely  contain  tyrotoxicon,  which  develops  under  those  circum- 
stances most  conducive  to  fermentative  changes  generally — 
viz.,  warmth  and  moisture,  impure  and  confined  air,  and  deficient 
light.  It  is  a  diazo-benzene-butyrate,  and  is  found  to  occur 
under  conditions  of  improper  storage  in  the  various  food  articles 
above  mentioned;  and  when  the  ingestion  of  any  of  these  articles 
has  given  rise  to  serious  consequences,  then  a  search  should  be 
instituted  for  this  most  powerful  poison.  The  symptoms  it 
creates  commonly  pass  off  within  a  few  hours,  but  occasionally 
serious  consequences  have  arisen,  such  as  the  development  of 
symptoms  akin  to  atropine  poisoning,  which  may  be  followed 
by  fatal  collapse.  The  physical  characters  of  the  article  are  not 
necessarily  altered  in  any  way,  but  acidity  is  always  marked,  and 
where  this  is  normally  present  (as  in  cheese)  it  is  invariably 
increased. 

The  method  of  examination  in  the  case  of  milk  is  as  follows : 


POISONING    BY    FOOD  3^9 

1.  The  filtrate  from  the  milk  is  first  n^ndercMl  distinctly  alkaline 
by  means  of  sodimTi  carbonate;  then  an  equal  bulk  of  pure  ether 
is  added,  and  the  whole  well  shaken  up  in  a  separator. 

2.  The  mixture  is  next  allowed  to  stand  until  all  the  ether  has 
separated  into  a  layer  upon  the  surface. 

3.  This  ethereal  layer  is  then  decanted  on  to  a  saucer,  where 
it  is  left  until  the  ether  has  spontaneously  evaporated  and  a 
comparatively  dry  residue  remains. 

4.  The  residue  is  carefully  dissolved  in  a  little  pure  water  and 
then  filtered  to  free  it  from  fat. 

5.  The  filtrate  is  next  well  shaken  with  an  equal  bulk  of  pure 
ether,  and  the  ethereal  layer,  having  separated,  is  removed  and 
allowed  to  again  evaporate  spontaneously. 

6.  The  residue  left  upon  the  saucer  will  then  contain  any 
tyrotoxicon  which  may  have  been  originally  present,  sufficiently 
pure  to  respond  to  the  following  test :  on  the  addition  of  a  few 
drops  of  a  mixture  of  equal  parts  of  pure  carbolic  and  sulphuric 
acids,  if  the  poison  be  present,  a  reddish  colour  appears. 

In  the  case  of  cheese  and  butter,  these  are  first  thoroughly 
worked  up  (triturated)  with  water,  and  the  filtered  extract  is 
then  treated  in  the  manner  indicated  above.  It  is  probable  that 
cheese  poisoning  is  usually  due  to  toxines  produced  by  bacteria. 

In  order  to  investigate  cases  of  alleged  food  poisoning  a  con- 
siderable amount  of  the  suspected  material  is  necessary.  Perish- 
able articles  should  be  placed  in  an  ice-box.  The  amount 
generally  submitted  for  examination  is  often  too  small  to  admit 
of  a  thorough  bacteriological  and  chemical  examination.  The 
bacteriological  evidence  will  be  furnished  by  the  morphological 
characters  of  the  organisms  found  in  the  food,  or  the  sufferer's 
vomit,  fgeces,  etc.,  their  pathogenicity,  and  serum  reactions. 
With  respect  to  the  chemical  examination,  that  will  be  concerned 
more  particularly  with  the  nature  and  amount  (if  present)  of 
chemical  preservative,  metallic  contamination,  or  colouring 
agent;  little  is  to  be  gained  by  testing  for  the  presence  and 
attempting  to  define  the  nature  of  "  ptomaines." 

Rats  and  mice  should  be  fed  with  portions  of  the  sample,  while 
other  animals — e.g.,  guinea-pigs— should  be  inoculated  subcu- 
taneously  and  intraperitoneally  from  cultures  and  also  from  the 
broth  emulsions  of  the  food.  If  any  of  the  animals  die,  a  com- 
plete post-mortem  examination  should  be  made. 

It  is  also  advisable  to  cut  sections  and  otherwise  microscopi- 


310  LABORATORY    WORK 

callv  examine  the  meat  to  see  if  the  bacilli  are  chiefly  on  the 
surface,  and  also  if  the  meat-fibres  arc  from  apparently  healthy 
animals. 

An  autopsy  should  be  made  in  all  cases  of  death  from  food 
poisoning  of  this  nature,  and  cultures  made  from  the  different 
organs  (spleen,  mesenteric  glands,  intestines,  etc.). 

As  already  mentioned,  the  agglutinative  properties  developed 
in  the  blood  of  suspected  cases  (sufferers  or  carriers)  should  be 
made  use  of  for  diagnostic  purposes. 

The  alkaloidal  products  of  putrefaction  are  separable  by  their 
relative  solubility  in  alcohol,  ether,  chloroform,  etc. 

The  following  method  (after  Stas)  may  be  adopted : 

The  finely  mixed  material  is  drenched  with  90  per  cent,  alcohol, 
tartaric  acid  is  next  added  until  the  liquid  is  definitely  acid  (if 
the  fluid  is  already  acid  this  is  not  necessary),  and  the  mixture 
is  then  allowed  to  digest  for  several  hours  at  70°  to  75°  C.  After 
cooling,  the  alcoholic  liquid  is  removed  (the  last  portions  by 
pressure)  and  filtered.  This  operation  is  repeated  several  times, 
and  the  united  filtrates  are  evaporated  in  vacuo  at  35°  C.  to  a 
small  bulk.  The  liquid  is  then  filtered  through  a  wet  filter 
to  remove  fatty  matter,  powdered  glass  is  now  added  to  the 
filtrate,  and  the  mixture  evaporated  nearly  to  dryness  over 
sulphuric  acid  in  a  vacuum.  The  residuum  is  next  digested  in 
pure  alcohol  for  twenty-four  hours,  and  again  evaporated  (at 
35°  C.  in  vacuo)  to  dryness.  This  residue  is  dissolved  in  a  little 
water  made  alkaline  with  sodium  bicarbonate,  and  the  solution 
is  then  well  shaken  with  4  volumes  of  pure  ether.  Finally,  the 
ethereal  solution  is  decanted,  evaporated  to  dryness,  and  the 
alkaloid  is  left  behind. 

The  extract  which  may  thus  be  obtained  may  be  dissolved 
and  tested  with  various  reagents  in  order  to  ascertain  its  par- 
ticular nature;  or  it  may  be  given  to  a  lower  animal  and  its 
effect  noted,  if  it  is  only  necessary  to  learn  whether  the  original 
material  was  harmful  or  not.  The  best  animals  for  such  ex- 
perimental purposes  are  mice. 

A  quantitative  and  qualitative  bacteriological  examination  of 
oysters  and  other  shellfish  is  often  very  desirable  in  the  interests 
of  public  health,  to  see  how  far  they  are  free  from  excretal 
and  sewage  pollution  bacteria.  The  most  thorough  method 
(Houston)  for  the  bacteriological  examination  of  oysters  is 
briefly  as  follows: 


POISONING    BY    FOOD  3^^^ 

I  The  outsides  of  the  oyster-shells  are  well  scrubbed  with 
soap  and  water,  and  cleaned  as  thoroughly  as  possible  in  running 
tap-water,  finally  with  sterile  water.  _ 

o  Hands  of  the  investigator  are  thoroughly  cleaned,  washed  in 
I  in  1,000  corrosive  sublimate  solution,  and  finally  with  sterile 

3  Oysters  opened  by  a  sterile  knife  held  in  position  by  a  sterile 
cloth  and  with  concave  shell  underneath.  Great  care  must  be 
taken  to  avoid  any  loss  of  the  liquor.  The  liquor  m  the  shell 
is  poured  into  a  sterile  i,ooo  c.c.  cylinder,  and  the  oyster  and 
oyster  liquor  are  added  after  the  oyster  has  been  cut  into  small 
pieces  by  sterile  scissors. 

4.  Ten  oysters  are  to  be  treated  as  above  m  each  experi- 
ment. T      _CC  1  11 

5  The  volume  of  oyster  +  oyster  liquor  is  read  off,  and  usually 
varies  between  8o  and  120  c.c.  For  qualitative  work  100  c.c. 
may  therefore  be  taken  as  a  fair  average  of  the  total  shell  contents 

of  ten  oysters.  ^      .u 

Sterile  water  is  then  poured  into  the  cyhnder  up  to  the 
I  000  c  c.  mark,  and  the  whole  well  stirred  with  a  sterile  rod. 
Each  100  c.c.  of  this  liquor  may  be  considered  to  contain  the 
bacteria  in  one  oyster. 

6  Various  amounts  and  fractions  of  this  liquor  are  used  for 
the  examination  for  B.  coli,  B.  enieritidis  sforogenes,  and  for 

streptococci.  tt      +  a 

For  the  B.  enieritidis  sporogenes  examinations  Houston  used 
10  I  o-i  o-oi,  o-ooi  c.c,  and  for  B.  coli  these  dilutions,  and  m 
addition  100  c.c.  and  ooooi  c.c.  He  made  these  primary  cultures 
in  triplicate,  and  required  at  least  two  out  of  the  three  to  be 
positive  for  a  preliminary  numerical  diagnosis. 

Cockles  and  mussels  may  be  examined  by  a  very  similar 

procedure. 

Ice-Cream.— There  is  a  considerable  probability,  and  some 
evidence,  that  ice-cream  may  be  a  means  of  spreadmg  disease, 
particularly  typhoid  fever.  In  investigating  such  a  possibility 
the  bacteriological  examination  of  ice-cream  is  of  value. 

The  ice-cream  should  be  collected  in  a  sterile  vessel— ^.g.,  a 
wide-mouth  sterile  bottle  with  glass  stopper— and  packed  m  ice 
if  it  cannot  be  examined  at  once. 

To  examine,  melt  the  ice-cream  by  placing  for  fifteen  to  twenty 
minutes  in  the  22°  C.  incubator,  then  treat  as  a  milk  sample. 


3T2  LABORATORY    WORK 

Edible  and  Poisonous  Fungi,  -With  a  viow  to  enable  residents 
in  tlie  coiHitry  to  distinguish  between  tlie  poisonous  and  edible 
kinds  of  fungi,  and  to  utilize  to  a  greater  extent  those  varieties 
which  are  useful  as  food,  the  Board  of  Agriculture  and  Fisheries 
has  published  a  small  book  of  illustrations  of  those  species  which 
are  more  commonly  found  in  Great  Britain,  together  with  brief 
descriptions  of  them.  It  is  pointed  out  in  this  publication  that, 
contrary  to  popular  belief,  the  poisonous  kinds  of  fungi  are  com- 
paratively few  in  number,  while  there  are,  on  the  other  hand, 
some  fifty  species  of  edible  fungi  which  may  safely  be  eaten. 
In  order  to  recognize  with  certainty  these  different  kinds,  it  is 
necessary  to  know  those  special  features  possessed  by  each 
species  which  separate  it  from  all  others.  The  rule-of-thumb 
signs  for  discriminating  between  edible  and  poisonous  fungi  are 
valueless,  and  no  reliance  should  be  placed  on  the  presence  of  a 
skin  that  is  readily  peeled  off  as  an  indication  of  an  edible  fungus, 
or  on  the  statements  that  a  silver  spoon  placed  in  contact  with 
poisonous  kinds  becomes  tarnished,  and  that  all  fungi  growing  on 
wood  are  poisonous. 

In  England  and  France  most  of  the  cases  of  fungus  poisoning 
which  have  been  reported  are  due  to  Amanita  phalloides.  Mus- 
carin  is  the  toxine  to  which  mushroom  poisoning  has  been  com- 
monly ascribed,  but  the  poison  of  this  fungus  is  probably  a 
toxalbumin.  Amanita  -phalloides  is  white  beneath  the  cap,  with 
a  yellowish-white  or  greenish-white,  shining  top;  and  the  stem, 
which  is  white  and  smooth,  is  bulbous,  and  is  clothed  at  its  upper 
part  with  an  expanded  pendant  ring.  It  usually  occurs  in 
woods,  and  it  rarely,  if  ever,  grows  far  away  from  trees,  having  a 
preference  to  the  proximity  of  the  oak  variety  of  tree.  The 
fungus  peels  almost  as  well  as  the  common  mushroom. 

Horse-Flesh. 

In  horse-fiesh  the  meat  is  darker  and  more  brownish;  it  is 
coarser  (the  muscular  fasciculi  being  broader)  than  in  ox-flesh; 
the  odour  of  the  fresh  meat  is  different,  and  after  the  lapse  of  a 
day  or  two,  as  the  flesh  dries,  it  develops  a  peculiar  faint  odour, 
a  bluish  sheen,  and  imparts  a  soapy  feeling  to  the  fingers.  The 
fat  is  more  yellow  and  soft,  and  possesses  a  sickly  taste;  and,  in 
consequence,  it  is  sometimes  removed  and  replaced  by  ox-fat, 
which  is  skewered  on  to  the  meat.     If  the  bones  have  not  been 


HORSE-FLESH  31 3 

removed,  they  wi]]  afford  an  additional  clue,  inasmucli  as  they  are 
larger  and  their  extremities  (tuberosities,  etc.,  for  the  attachment 
of  muscles  and  ligaments)  are  larger  and  more  marked;  there  are, 
in  addition,  some  anatomical  differences  in  the  construction  of 
the  horse's  skeleton.  In  cattle  the  breast-bone  is  broad  and 
flattened,  while  in  the  horse  the  front  portion  is  keel-shaped. 
The  ribs  in  cattle  are  flatter  and  broader  in  the  middle  and  lower 
thirds  than  in  the  horse. 

Horse-flesh  is  richer  in  glycogen  than  ordinary  meat,  and  as 
this  remains  unchanged  for  a  long  time  it  is  taken  advantage  of 
in  the  following  test : 

An  infusion  of  the  suspected  meat  is  prepared  by  boiling 
100  grammes  of  it,  in  a  finely  minced  condition,  with  |  litre  of 
water,  for  nearly  one  hour;  the  broth  is  then  concentrated  to 
about  100  c.c,  and  is  mixed,  when  cold,  with  dilute  nitric  acid 
in  the  proportion  of  5  c.c.  to  loo  c.c.  of  the  broth;  it  is  then 
filtered  and  tested  with  hot  (freshly  prepared)  saturated  solution 
of  iodine,  gently  let  down  upon  it  so  as  not  to  mix  the  liquids. 
If  the  substance  is  horse-flesh,  a  marked  reddish  or  brownish-violet 
ring  appears  at  the  junction  of  the  two  liquids.  If  a  deep  violet 
colour  results,  starch  is  present,  as  may  be  the  case  in  sausage- 
meat.  The  iodine  solution  should  consist  of  iodine,  i  gramme; 
iodide  of  potassium,  2  grammes;  water,  lOO  c.c;  and  it  must  be 
carefully  added,  since  a  slight  excess  changes  the  colour  to 
reddish-brown .  Glycogen  is  present  in  the  livers  of  cattle  and  in 
meat  extract,  and  the  dextrines  derived  from  starch  in  sausages 
give  a  similar  reaction;  therefore  it  is  only  when  the  amount 
found  is  considerable  that  the  glycogen  reaction  can  be  taken  as 
certain  evidence  of  horse-flesh  in  sausages.  Moreover,  in  old 
sausages  containing  horse-flesh  the  glycogen  is  liable  to  undergo 
decomposition,  and  then  no  reaction  is  obtained.  In  smoked 
horse-flesh  the  glycogen  is  destroyed. 

Certain  organs  of  the  horse  are  occasionally  sold  as  the  corre- 
sponding organs  of  the  ox.  The  tongue  of  the  horse  is  broad 
and  rounded  at  its  free  end,  instead  of  pointed,  as  in  the  ox; 
and  it  is  smooth  at  the  base,  where  the  tongue  of  the  ox  is  rough 
with  prominent  papillae.  If  the  hyoid  bone  is  attached,  it  is 
found  to  be  made  up  of  five  parts,  whereas  that  of  the  ox  consists 
of  nine.  The  epiglottis  is,  moreover,  smaller  and  more  pointed 
in  the  horse.  The  liver,  whether  of  the  ox  or  sheep,  consists  of 
one  very  large  lobe,  and  another  relatively  small  one;  in  the 


314  LABORATORY   WORK 

horse  tliero  arc  three  large  and  distinct  lolios,  and  a  fourth  which 
is  very  small,  and  there  is  no  gall-bladder. 

The  kidney  of  the  horse  is  more  heart-shaped,  and  cannot 
be  mistaken  for  the  long  lobulated  kidney  of  the  ox.  The  heart 
of  the  horse  differs  from  that  of  the  ox  in  being  less  conical ;  it 
is  also  darker,  softer,  and  has  less  fat  at  its  base.  There  is  a  bone 
in  tlie  heart  of  the  ox  (os  cordis). 

Sausages. 

These  are  made  of  the  chopped  flesh  or  internal  organs  of 
various  animals,  mixed  with  condiments,  flour,  bread,  or  potato 
meal,  and  filled  into  clean  gut  or  parchment;  the  sausages  are 
then  generally  boiled,  smoked,  or  scalded.  Saltpetre  is  some- 
times added  to  furnish  a  good  red  colour  to  the  meat,  and  often 
colouring  agents  (carmine,  cochineal,  or  aniline)  and  preservatives 
are  added.  The  colouring  matter  can  generally  be  extracted 
by  warming  for  several  hours  with  a  mixture  of  equal  parts  of 
glycerine  and  water.  Boric  acid  is  often  used  as  a  preservative. 
It  is  certain  that  since  boric  acid  prevents  objective  decom- 
position, such  as  is  detectable  by  odour,  it  permits  of  the  use  of 
stale  meat  and  meat  in  the  early  stages  of  decomposition  for  the 
making  of  sausages.  Dr.  C.  A.  MacFadden,  in  a  Report  to  the 
Local  Government  Board  (1908)  expresses  the  view  that  if  boron 
preparations  are  permitted,  0-25  per  cent.  (17-5  grains  per  pound) 
of  boric  acid  should  not  be  exceeded,  and  that  even  then  such 
addition  should  be  made  known  to  the  purchaser. 

The  use  of  antiseptics  in  sausages  is  to  be  discouraged.  Even 
the  boric  acid,  which  is  most  frequently  employed,  may  be 
injurious  to  those  with  weak  stomachs  or  kidneys.  Meat 
sausages  (pork  and  otherwise)  can  be  made,  sold,  and  consumed 
without  any  such  addition,  if  good  fresh  material  is  employed, 
for  people  do  not  purchase  sausages  to  store  in  the  house ;  and 
the  dried  "  German  "  sausages  can  be  sufficiently  preserved  by 
other  means. 

While  the  amounts  of  boric  acid  usually  employed  will  not 
enable  the  use  of  meat  which  has  reached  a  stage  of  marked 
putrefaction,  they  permit  of  the  use  of  stale  material  in  a  state  of 
incipient  decomposition,  and  while  they  may  reduce  the  danger 
from  putrefactive  toxines,  they  do  not  materially  reduce  the  risks 
of  poisoning   from   organisms  of  the   Gaertner  group  or  from 


SAUSAGES  315 

Bacillus  hoiulimis.  Owing  to  its  cheapness  (beef  sausages  arc 
generally  sold  at  about  5d.  a  pound),  the  poorer  people  consume 
a  considerable  quantity  of  sausage,  f  pound  of  which  could  be 
eaten  at  a  meal  by  an  adult.  That  the  use  of  chemical  antiseptics 
is  unnecessary  is  demonstrated  by  the  large  number  of  makers 
who  never  employ  them.  The  writer  has  satisfied  himself,  by 
experiments,  that  if  the  meat  is  sound  and  fresh  at  the  time  it  is 
put  into  a  sausage  it  will  keep  in  hot  weather  for  forty-eight  hours, 
and  that  as  little  as  12  grains  of  boric  acid  to  the  pound  will  enable 
the  sausage  to  be  kept  in  such  weather  for  four  days ;  so  that  even 
if  antiseptics  are  permitted,  and  it  is  necessary  to  keep  fresh 
sausages  for  four  days,  there  is  no  case  for  the  employment  of 
the  20  to  30  grains  of  boric  acid  to  the  pound  which  is  sometimes 
found  to  be  present. 

It  is  not  a  difficult  matter  to  detect  early  decomposition  in 
sausages ;  the  alteration  in  the  odour  will  sometimes  suffice ; 
for  if  a  little  of  the  sausage  is  boiled  with  water  and  some  freshly 
prepared  lime-water  is  added,  good  meat  yields  only  a  faint 
ammoniacal  odour,  whereas  bad  meat  will  give  off  a  peculiarly 
offensive  ammoniacal  odour.  Putrefaction  generally  commences 
in  the  middle  of  the  sausage,  when  a  dirty  greyish-green  colour  is 
often  to  be  noted. 

The  skins  of  sausages  have  been  known  to  contain  mineral 
poisons,  but  this  is  very  rare. 

Eggs. 

The  best  tests  for  bad  and  stale  eggs  are  the  following: 

1.  Fresh  eggs  are  most  translucent  towards  their  centres  if 
held  vertically  against  the  light ;  stale  eggs  are  most  translucent 
at  their  upper  extremities. 

2.  If  2  ounces  of  salt  are  dissolved  in  a  pint  of  water,  fresh 
eggs  when  placed  in  the  solution  sink,  and  stale  ones  float. 

Opaque  spots  are  generally  due  to  moulds  that  have  gained 
access  through  a  crack  or  cracks  in  the  shell,  or  to  embryos. 
Eggs  generall.y  contain  bacteria  and  sometimes  parasitic  worms, 
but  there  are  no  recorded  instances  of  human  infection. 

Toxic  poison  has  been  separated  from  decomposing  eggs. 

Meat  Preparations. 

Many  meat  extracts  are  now  upon  the  market,  the  tendency 
being  for  the  public  to  over-estimate  their  food  value.  They 
consist  of  the  extractives  of  meat,  and  not  of  the  meat  itself; 


3t6  laboratory  work 

and  they  act  as  stimulants  and  regulators  of  digestion  rather  than 
as  true  foods  capable  of  providing  the  necessary  amount  of 
nitrogenous  material  for  tlie  needs  of  the  body. 

A  meat  extract  should  consist  of  a  golden-brown  sticky  sub- 
stance, with  a  pleasant  meaty  odour.  It  should  never  be  hard, 
and  should  attract  moisture  strongly  from  the  air.  The  reaction 
should  be  slightly  acid.  The  usual  method  of  preparation 
consists  in  heating  raw  meat,  which  has  been  finely  divided,  with 
a  little  water  under  pressure.  The  extract  thus  made  is 
filtered  and  evaporated  in  vacuo.  It  is  essential  that  a  tem- 
perature below  75°  C.  be  employed  if  all  gelatine  is  to  be 
excluded  (Beveridge).  The  extract  thus  made  contains  the 
flesh  bases  or  extractives  and  mineral  matters  of  the  meat,  and 
is  free  from  albumin,  meat  fibre,  gelatine,  and  fat;  but  in  some 
of  the  meat  extracts  on  the  market  these  substances  and  also 
vegetables  are  subsequently  added  in  order  to  give  the  extract  a 
certain  food  value.  Meat  juices  are  prepared  in  the  cold  by 
subjecting  finely  divided  meat  to  strong  pressure,  and  ultimately 
concentrating  by  evaporation  in  vacuo.  They  contain  the 
soluble  proteins  of  meat. 

Protein  matter  constitutes  the  bulk  of  meat  extract,  but 
it  varies  greatly  in  amount  in  different  samples.  The  total 
nitrogen,  calculated  as  protein,  should  not  be  less  than  55  per 
cent.,  of  which  not  less  than  25  per  cent,  must  be  insoluble 
in  alcohol.  Protein  soluble  in  alcohol  is  presumed  to  consist  of 
half  meat  bases  and  half  meat  extract,  but  from  a  practical  point 
of  view  these  distinctions  are  unnecessary  in  routine  examina- 
tions. Water  should  not  exceed  25  per  cent,  and  the  ash  20  per 
cent.;  the  former  varies  from  14  to  25  per  cent.,  and  the  latter 
from  14  to  33  per  cent.,  in  samples  of  the  usual  brands  of  meat 
extracts. 

Meat  Essences. — ^A  meat  essence  is  a  more  liquid  extract, 
containing  more  water,  but  has  the  same  colour,  odour,  and 
reaction.  Protein  matter  should  not  be  less  than  9  percent.,  of 
which  not  less  than  7  per  cent,  should  be  insoluble  in  alcohol. 
Water  should  not  exceed  90  per  cent.,  nor  the  mineral  ash  1-5 
per  cent. 

The  analysis  of  a  meat  essence  is  similar  to  that  of  a  meat 
extract,  about  ten  times  as  much  of  the  substance  being  taken 
for  each  examination. 

On  account  of  the  large  amount  of  water  present,  frothing  of 


MEAT   PREPARATIONS  317 

the  contents  of  the  Kjeldahl  flask  is  apt  to  be  troublesome,  and 
unless  the  first  stage  of  the  process  is  carefully  watched  the  fliusk 
contents  may  be  ejected. 

The  gelatine  in  table  jellies  usually  amounts  to  from  13  t(j  i'] 
per  cent.,  so  that  what  nutrient  value  they  possess  is  derived 
mainly  from  the  sugar,  which  amounts  to  from  50  to  80  per  cent. 
W.  W.  O.  Beveridge  gives  the  following  method  for  obtaining  a 
closely  approximate  estimation  of  gelatine : 

Twenty-five  grammes  of  the  material  containing  gelatine  are 
dissolved  in  hot  water,  and  filtered  if  necessary  to  remove  any 
insoluble  matter.  The  solution  is  evaporated  to  a  thick  syrup  on 
the  water-bath  in  a  platinum  capsule,  then  removed  and  cooled ; 
5  c.c.  of  a  10  per  cent,  solution  of  formaldehyde  is  then  added, 
which  renders  the  gelatine  insoluble.  Other  proteins  must  not  be 
present.  The  soluble  matters,  such  as  sugar,  etc.,  are  dissolved 
out  by  means  of  boiling  water,  when  the  gelatine  remaining  behind 
can  be  dried  and  weighed. 


CHAPTER  IX 

ALCOHOLIC  BEVERAGES 

The  law  allows  a  margin  of  2  per  cent,  of  proof-spirit  before 
regarding  a  beverage  as  an  alcoholic  fluid . 

The  estimation  of  alcohol  in  alcoholic  beverages  may  be  made 
as  follows : 

Three  hundred  c.c.  of  the  beverage  (generally  diluted)  is  placed 
in  a  retort  and  boiled  gently  until  about  200  c.c.  have  distilled 
over  into  a  flask.  The  distillate  is  next  made  up  to  the  original 
bulk  of  300  c.c.  with  distilled  water,  and  the  specific  gravity  is 
taken  in  a  S.G.  bottle,  when  the  temperature  has  cooled  to  about 
15°  C.  If  this  is  1,000  the  fluid  is  free  from  alcohol,  and  the 
amount  of  alcohol  which  has  distilled  over  will  be  great  in  pro- 
portion to  the  extent  to  which  the  S.G.  falls  below  1,000,  since 
pure  absolute  alcohol  at  15°  C.  has  a  S.G.  of  793-8.  To  find  the 
percentage  amount  of  alcohol  from  the  S.G.  of  the  distillate,  the 
alcohol  table  on  pp.  320  and  321,  in  which  these  data  are  arranged 
side  by  side,  may  be  consulted. 

In  estimating  alcohol  in  spirit,  take  100  c.c.  of  the  spirit,  and 
dilute  with  200  c.c.  of  distilled  water.  Before  commencing  the 
distillation  of  beer,  it  should  be  well  shaken  to  expel  as  much 
carbonic  acid  as  possible,  passed  through  a  coarse  filter  paper, 
diluted  with  an  equal  volume  of  water,  and  rendered  alkaline 
with  caustic  soda;  and  as  a  further  precaution  against  the  beer 
frothing  over,  a  small  flame  only  should  be  applied  to  the  flask 
and  a  little  tannin  powder  may  be  added. 

An  estimation  may  be  made  without  distillation  in  the  fol- 
lowing manner:  Ascertain  the  specific  gravity  at  15°  C.  of  the 
original  liquid,  then  take  300  c.c.  and  boil  down  to  about  100  c.c, 
thus  driving  off  the  alcohol;  make  up  to  the  original  bulk  with 
distilled  water,  and  again  take  the  S.G.  at  15°  C.  The  difference 
between   the   first   and   second   gravities   deducted   from    1,000 

318 


SPIRITS  319 

(the  gravity  of  water)  gives  the  S.G.  of  the  alcohol  evaporated. 
If,  for  instance,  the  first  S.G.  of  a  sample  of  beer  is  1,009  '"^^^^  the 
second  S.G.  is  1,018,  then  1,018-1,009  =  9,  '"^^^^  1,000 -(j  (/ji. 
A  reference  to  the  table  on  p.  320  will  sliow  that  a  liquid  with  a 
S.G.  of  991  (or  0-991,  as  there  expressed)  contains  6-55  per  cent, 
of  alcohol  by  volume. 

Spirits. 

Spirits  constitute  the  distillates  from  various  liquids  containing 
alcohol  derived  from  grain. 

The  expressions  "  over  proof,"  "  proof,"  and  "  under  proof," 
are  commonly  employed  to  denote  the  amount  of  alcoliol  in 
spirits.  The  above  terms  had  their  origin  in  a  former  practice 
of  pouring  the  spirit  over  gunpowder,  and  applying  a  light  to  it. 
If  the  spirit  burned  without  igniting  the  powder,  owing  to  the 
large  admixture  oi  water,  it  was  "  under  proof  " ;  and  the  weakest 
spirit  capable  of  firing  the  powder  was  called  "proof."  Such  a 
spirit  was  stronger  than  the  present  "  proof -spirit,"  for  by 
"  proof -spirit  "  is  now  implied  a  mixture  of  57*06  per  cent,  by 
volume,  or  49-24  per  cent,  by  weight,  of  pure  absolute  alcohol  in 
water,  with  a  S.G.  of  0-9198  at  15°  C;  and  solutions  weaker  or 
stronger  than  this  are  "  under  "  or  "  over  "  proof. 

The  proportions  of  alcohol  in  alcoholic  fluids  may  be  stated  as 
either  a  percentage  of  alcohol  by  weight,  a  percentage  of  alcohol 
by  volume,  or  as  a  percentage  of  proof -spirit. 

The  percentage  of  alcohol  by  weight  may  be  obtained  by 
multiplying  the  percentage  by  volume  by  0-7938  and  dividing 
the  product  by  the  specific  gravity;  and,  conversely,  the  per- 
centage of  alcohol  by  volume  may  be  obtained  by  multiplying 
the  percentage  by  weight  by  the  specific  gravity,  and  dividing 
the  product  by  0-7938. 

The  percentage  of  proof -spirit  may  be  obtained  by  multiplying 
the  percentage  of  alcohol  by  volume  by  175.  A  percentage  of 
proof -spirit  is  always  expressed  by  volume. 

The  Sale  of  Food  and  Drugs  Acts  fix  the  following  low  limits 
of  alcohol  in  "  spirits."  Brandy,  whisky,  and  rum  may  be  25° 
"under  proof,"  corresponding  to  75  per  cent,  of  proof -spirit — 
i.e.,  the  S.G.  may  be  as  high  as  0-9474 — and  there  may  be  only 
42-8  per  cent.,  by  volume,  of  absolute  alcohol. 

Gin  may  be  35°  "  under  proof  "■ — i.e.,  may  only  contain  37-1 
per  cent,   by  volume  of   absolute  alcohol;   and  the  S.G.   may 


320 


LABORATORY   WORK 


be  as  high  as  09563,  corresponding  to  65  per  cent,  of  proot- 
spirit. 

Suppose  a  sample  of  whisky  is  44""  under  proof;  it  therefore 
contains  100  - 44=  56  per  cent,  of  proof-spirit.  What  percentage 
of  spirit  of  25°  under  proof  does  it  contain  ?  A  spirit  of  25° 
under  proof  contains  75  per  cent,  of  proof-spirit.     Therefore  the 

whisky  contains  -^-^^^^=74*6  per  cent,  of  spirit  of  required 

75 
strength  and  25  4  per  cent,  of  added  water. 

The  percentage  amount  by  weight  of  absolute  alcohol  generally 
present  in  spirits=32  to  50;  wines=8  to  18  (about  10  per  cent, 
in  clarets);  strong  ales  and  porter=5  to  8;  small  beer=2  to  3. 
Lager  beer  contains  more  dextrine  than  English  beer,  and  usually 
less  alcohol. 

Short  Alcohol  Table. 


Specific 

Gravity  at 

15°  C. 

0  >. 

it 

3 

0  rt 

0  >> 

Per  Cent, 
under  Proof. 

Specific 

Gravity  at 

15°  c. 

Per  Cent,  of 
Alcohol  by 
Volume. 

Per  Cent, 
under  Proof, 

I '000 

0-00 

lOO-OO 

0-972 

24-08 

57-80 

0-944 

44-79 

21-50 

0-999 

0-66 

98-84 

0-971 

25-07 

56-06 

0-943 

45-41 

20-43 

0-998 

1-34 

97-60 

0-970 

26-04 

54-37 

0-942 

46-02 

19-36 

0-997 

2-12 

96-29 

0-969 

26-95 

52-77 

0-941 

46-59 

i8-:i6 

0-996 

2-86 

95-00 

o-96b 

27-86 

51-18 

0-940 

47-13 

17-40 

0-995 

3-55 

93-78 

0-967 

2S-77 

49-60 

0-939 

47-67 

16-46 

0-994 

4-27 

92-50 

0-960 

29-67 

48-00 

0-938 

48-21 

15-50 

0-993 

5-00 

91-23 

0-965 

30-57 

46-44 

0-937 

48-75 

14-57 

0-992 

578 

89-87 

0-964 

31-40 

44-97 

0-936 

49-29 

13-63 

0-991 

6-55 

88-50 

0-963 

32-19 

43-60 

0-935 

49-81 

12-70 

0-990 

7-32 

87-16 

0-962 

32-98 

42-20 

0-934 

50-31 

11-82 

0-989 

8-i8 

85-65 

0-961 

33-81 

40-74 

0-933 

50-82 

10-94 

0-988 

9.04 

S4-15 

0-960 

34-54 

39-47 

0-932 

51-32 

10-05 

0-987 

9-86 

82-70 

0-959 

35-28 

38-18 

0-931 

51-82 

9-20 

0-986 

IO-73 

81-20 

0-958 

36-04 

36-83 

0-930 

52-29 

8-36 

0-985 

11-61 

79-65 

0-957 

36-70 

35-68 

0-929 

52-77 

7-52 

0-984 

12-49 

78-10 

0-950 

37-34 

34-57 

0-928 

53-24 

6-70 

0-983 

13-43 

76-46 

0-955 

38-04 

33-32 

0-927 

53-72 

5-86 

0-982 

M-37 

74-82 

0-954 

38-75 

32-08 

0-926 

54-19 

5-03 

0-981 

15-30 

73-18 

0-953 

39-47 

30-84 

0-925 

54-66 

4-20 

0-980 

16-24 

71-54 

0-952 

40-14 

29-66 

0-924 

55-13 

3-38 

0-979 

17-17 

69-90 

0-951 

40-79 

28-52 

0-923 

55-60 

2-56 

0-978 

18-25 

68-00 

0-950 

41-32 

27-60 

0-922 

56-07 

1-74 

0-977 

19-28 

66-20 

0-949 

41-84 

26-67 

0-921 

56-54 

0-92 

0-976 

20-24 

64-53 

0-948 

42-40 

25-70 

0-920 

56-98 

0-14 

0-975 

21-19 

62-87 

0-947 

42-95 

24-74 

0-9198 

57-06 

-Proof 

0-974 

22-18 

61-13 

0-946 

43-56 

23-66 

0-973 

23-10 

59-52 

0-945 

44-18 

22-58 

SPIRITS 


321 


Short  Alcohol  Table — continued. 


"o  >> 

w 

"0  >■ 

"o  >> 

0  rt 

■  XI  .: 

c's 

0  ^ 

.-^  »i 

tio 

0  « 

•■°  V 

<i  0 

'^6 

Per  Cent 

Alcohol 

Volume 

S  2 

>-  u 
(L)  a> 

^% 
0-68 

Specifi 
Gravity 

15°  c. 

Per  Cent 

Alcohol 
Volume 

C   0 
V  <u 

"^0 

S 

0-919 

57-45 

0-876 

75-45 

32-23 

0-833 

90-29 

58-23 

0-918 

57-92 

1-51 

0-875 

75-83 

32-89 

0-832 

90-58 

58-74 

0-917 

58-36 

2-28 

0-874 

76-20 

33-54 

0-831 

go-S8 

59-26 

0-16 

58-80 

3-05 

0-873 

76-57 

34-19 

0-830 

91-17 

59-77 

0-915 

59-22 

3-78 

0-872 

76-94 

34-84 

0-829 

91-46 

60-28 

0-914 

59-63 

4-50 

0-871 

77-29 

35-45 

0-828 

91-75 

60-79 

0-913 

60-07 

5-27 

0-870 

77-64 

36-07 

0-827 

92-05 

61-32 

0-912 

60-52 

6-07 

0-869 

78-00 

36-69 

0-826 

92-36 

61-86 

0-911 

60-97 

6-86 

0-868 

78-36 

37-33 

0-825 

92-66 

62-38 

0-910 

61-40 

7-61 

0-867 

78-73 

37-98 

0-824 

92-94 

62-88 

0-909 

61-84 

8-36 

0-866 

79-12 

38-65 

0-823 

93-23 

63-38 

0-908 

62-31 

9-20 

0-865 

79-50 

39-32 

0-822 

93-49 

63-84 

0-907 

62-79 

10-03 

0-864 

79-86 

39-96 

0-821 

93-75 

64-30 

0-906 

63-24 

10-84 

0-863 

80-22 

40-60 

0-820 

94-00 

64-74 

0-905 

63-69 

11-64 

0-862 

80-60 

41-26 

0-819 

94-26 

65-18 

0-904 

64-14 

12-41 

0-861 

8 1 -00 

41-96 

o-8i8 

94-51 

65-62 

0-903 

64-58 

13-18 

0-860 

81-40 

42-66 

0-817 

94-76 

66-07 

0-902 

65-01 

13-92 

0-859 

8i-8o 

43-35 

o-8i6 

95-03 

66-53 

0-901 

65-41 

14-62 

0-858 

82-19 

44-04 

0-815 

95-29 

67-00 

0-900 

65-81 

15-33 

0-857 

82-54 

44-66 

0-814 

95-55 

67-46 

0-899 

66-25 

16-11 

0-856 

82-90 

45-28 

0-813 

95-82 

67-92 

0-898 

66-69 

16-88 

0-855 

83-25 

45-90 

0-8l2 

96-08 

68-38 

0-897 

67-11 

17-61 

0-854 

83-60 

46-51 

o-8ii 

96-32 

68-80 

0-896 

67-53 

18-34 

0-853 

83-94 

47-11 

o-8io 

96-55 

69-20 

0-895 

67-93 

19-05 

0-852 

84-27 

47-70 

0-809 

96-78 

69-61 

0-894 

68-33 

19-74 

0-851 

84-60 

48-27 

o-8o8 

97-02 

70-03 

0-893 

68-72 

20-42 

0-850 

84-93 

48-84 

0-807 

97-27 

70-46 

0-892 

69-11 

21-11 

0-849 

85-26 

49-38 

o-8o6 

97-51 

70-88 

0-891 

69-50 

2I-7J 

0-848 

85-59 

50-00 

0-805 

97-73 

71-26 

0-890 

69-92 

22-53 

0-847 

85-94 

50-61 

0-804 

97-94 

71-64 

0-889 

70-35 

23-29 

0-846 

86-28 

51-21 

0-803 

98-16 

72-02 

0-888 

70-77 

24-02 

0-845 

86-61 

51-78 

0-802 

98-37 

72-40 

0-887 

71-17 

24-73 

0-844 

86-93 

52-34 

o-8oi 

98-59 

72-77 

0-886 

71-58 

25-44 

0-843 

87-24 

52-90 

o-8oo 

98-80 

73-14 

0-885 

71-98 

26-15 

0-842 

87-55 

53-43 

0-799 

98-98 

73-47 

0-884 

72-38 

26-85 

0-841 

87-85 

53-96 

0-798 

99-16 

73-81 

0-883 

72-77 

27-52 

0-840 

88-16 

54-50 

0-797 

99-35 

74-14 

0-882 

73-15 

28-19 

0-839 

88-46 

55-02 

0-796 

99-55 

74-50 

0-881 

73-54 

28-87 

0-838 

88-76 

55-55 

0-795 

99-75 

74-83 

o-88o 

73-93 

29-57 

0-837 

89-08 

56-10 

0-794 

99-96 

75-18 

0-879 

74-33 

30-26 

0-836 

89-39 

56-66 

Alcohol 

0-878 

74-70 

30-92 

0-835 

89-70 

57-20 

0-7938 

100-00 

75-25 

0-877 

75-08 

31-58 

0-834 

89-99 

57-71 

Brandy  is  spirit  derived  from  the  grape.  It  then  contains, 
besides  ordinary  ethyhc  alcohol,  a  number  of  secondary'  prod- 
ucts, including  organic  acids  (chiefly  acetic),  aldehydes  (com- 
pounds midway  between  alcohol  and  acid),   ethers   (of  which 


322  LABORATORY   WORK 

acetic  is  the  more  important),  furfural,  and  higher  alcohols 
(including  amylic,  which  constitutes  the  chief  constituent  of 
so-called  fusel  oil). 

The  Lancet  Analytical  Commission  found  brandy  to  have  the 
following  composition  (in  grammes  per  loo  litres  of  alcohol 
present) : 

Acidity  (in  terms  of  acetic  acid)  64  to  85  grammes. 

Aldehydes  10  to  14  grammes. 

Ethers  (in  terms  of  ethyl  acetate)  about  100  grammes. 

Furfural,  i-6  to  2 "6  grammes. 

The  alcoholic  strength  is  about  50  per  cent,  by  volume. 

Grain-spirit,  beet-spirit,  and  gin  contain  only  very  small  quan- 
tities of  ethers;  rum  contains  ethers  in  great  excess;  in  whisky 
the  ethers,  though  less,  more  nearly  approximate  to  brandy. 
The  proportions  of  other  secondary  products  vary  in  these  liquids 
from  those  of  genuine  brand3^ 

Spurious  brandy  is  mainly  derived  from  rye,  potatoes,  maize, 
barle^^  and  figs;  and  the  alcohol  may  be  distilled  over  in  either 
a  pot-still  or  patent-still.  The  pot-still  consists  of  a  body, 
termed  the  "  pot,"  with  a  long  neck  at  the  top.  The  neck  is 
connected  with  a  tortuous  pipe,  termed  the  "  worm,"  which,  by 
means  of  a  constant  stream  of  water,  acts  as  a  condenser.  The 
spirit  is  highly  rectified  by  the  patent  or  fractionating  still, 
whereby  secondary  products  are  almost  entirel}-  removed. 

The  raw  materials  employed  in  the  production  of  modern 
whisky  are  malt  and  grain  (chiefly  maize),  with  small  quantities 
of  wheat  and  oats;  and  the  fermentative  action  of  the  yeast,  by 
which  the  maltose  is  split  up  into  alcohol  and  carbonic  acid,  is 
pushed  to  the  extreme  limit,  with  the  object  of  converting  all 
the  sugar  into  alcohol.  Secondary  products  in  patent-still  whisky 
are  present  in  very  small  quantity,  but  they  are  greater  in  genuine 
pot-still  whiskies;  and  it  has  been  suggested  that  the  minimum 
"  coefficient"  of  secondary  products  in  the  latter  whiskies  should 
be  taken  at  380  parts  per  100,000  parts  of  absolute  alcohol,  and 
the  ethers  at  80. 

Furfural  gives  an  easily  obtained  and  very  distinct  colour 
reaction;  it  is  certainly  the  most  toxic  constituent  of  whisky. 
Besides  the  secondary  products  mentioned  above,  whisky  also 
contains  other  bodies,  concerning  the  chemical  nature  of  which 
we  are  ignorant,   and  it  is  probably  to  them  that  it  owes   its 


SPIRITS  323 

characteristic  taste  and  flavour.  Whisky,  therefore,  differs  from 
brandy  not  only  in  taste  and  flavour,  but  also  in  that  it  contains 
relatively  more  higher  alcohols  and  relatively  less  compound 
ethers;  it  further  contains  traces  of  empyreumatic  or  tarry  sub- 
stances derived  from  the  malting  process.  Concerning  the  thera- 
peutic action  of  the  secondary  products  in  brandy  and  whisky — 
namely,  the  higher  alcohols,  the  ethers  and  aldehydes — we  have 
very  little  exact  information;  but  some  authorities  maintain 
that  they  are  serviceable  for  medicinal  purposes. 

The  higher  alcohols  and  ethers  in  wine  are  generally  present 
in  much  the  same  ratio  as  in  brandy. 

The  ethers  present  in  genuine  brandy  usually  amount  to  about 
100  parts  per  100,000  of  the  absolute  alcohol  present.  (This 
method  of  calculating  on  the  absolute  alcohol  present  enables  a 
comparison  to  be  made  between  different  brandies  which  may 
vary  in  their  alcoholic  strength.) 

The  estimation  of  the  ethers  is  performed  as  follows:  Having 
obtained  the  distillate  and,  from  the  specific  gravity,  ascertained 
the  amount  of  alcohol  (as  previously  described),  a  drop  of 
phenolphthalein  solution  is  added  to  the  distillate,  and  any  free 
acid  that  may  have  come  over  with  the  alcohol  is  exactly  neu- 
tralized. It  is  then  transferred  to  a  hard  glass  boiling-flask, 
25  c.c.  of  ^  alcoholic  soda  added,  and  complete  saponification 
is  effected  under  a  reflex  condenser  in  about  two  hours.  Then, 
after  cooling,  titrate  the  excess  of  soda  with  ^^  hydrochloric  acid. 
Each  c.c.  of  soda  which  has  been  used  in  saponifying  the  ethers 
corresponds  to  0 -0088  gramme  of  ethyl  acetate.  It  is  desirable 
to  make  a  blank  experiment  with  pure  spirit. 

Furfural. — To  test  for  this,  10  c.c.  of  distillate  should  be 
diluted  to  50  per  cent,  of  alcohol,  and  placed  in  a  glass  cylinder. 
Ten  c.c.  of  standard  furfural  (0*005  gramme  per  litre)  is  placed 
in  a  similar  cylinder.  To  each,  10  drops  of  pure  colourless  aniline 
oil  and  i  c.c.  of  pure  acetic  acid  are  added.  Furfural  strikes  a 
bright  reddish-pink  colour  ;  and  after  fifteen  minutes  the  colour 
in  the  two  cylinders  may  be  compared  and  an  approximate 
estimate  of  the  furfural  in  the  spirit  thereby  arrived  at. 

Fusel  oil  is  a  mixture  of  oily  bodies  consisting  chiefly  of  pentylic 
or  amylic  alcohol,  and  is  a  constant  accompaniment  of  common 
alcohol.  It  is  a  product  which  appears  to  be,  bulk  for  bulk,  more 
injurious  than  ordinary  ethylic  alcohol;  and  it  shordd  not  be  per- 
mitted to  exceed  0*2  per  cent. 


324 


LABORATORY   WORK 


Acidity. — The  acidity  of  brandy  is  about  0*05  to  o-ii  per  cent., 
that  of  whisky  about  O'l  per  cent.,  and  that  of  rum  about  05 
per  cent. 

Detection   and   Estimation   of   Fusel  Oil 
(Amylic  Alcohol). 

The  presence  of  fusel  oil  may  also  be  detected  by  {a)  slowly 
distilling  off  the  great  bull:  of  the  hquid  and  extracting  the  residue 
in  the  flask  with  ether ;  the  ethereal  solution  is  allowed  to  evapo- 
rate spontaneously,  and  then  the  residue  is  heated  with  sulphuric 
acid  and  sodium  acetate,  when  the  odour  of  pear  is  evolved. 

(&)  By  decolorizing  with  animal  charcoal,  adding  a  few  drops 
of  hydrochloric  acid  and  afterwards  some  fresh  and  colourless 
aniline  oil;  in  the  presence  of  fusel  oil  the  aniline  compound 
acquires  a  rose  tint. 

Rose's  quantitative  estimation  is  based  on  the  following  facts: 
Cliloroform  possesses  the  property  of  rapidly  removing  amylic 


w 


FIG.    68. APPARATUS    FOR    ESTIMATING    FUSEL    OIL    BY    ROSE's    PROCESS. 

alcohol  from  its  solution  in  diluted  spirit,  and  the  presence  of 
amylic  alcohol  in  chloroform  increases  its  power  to  dissolve 
ethylic  alcohol.  When,  therefore,  chloroform  is  shaken  with 
diluted  ethylic  alcohol  containing  amyhc  alcohol,  there  will  be 
a  notable  increase  in  its  volume. 

The  apparatus  required  is  a  stoppered  tube  (Fig.  68),  capable 
of  holding  about  180  c.c,  having  the  lowered  part,  holding 
about  50  c.c,  drawn  out  and  graduated. 


WINE  325 

Twenty  c.c.  of  chloroform  are  introduced  into  tlio  bottom  part 
of  the  tube  by  means  of  a  long-necked  funnel,  so  that  it  shall 
not  collect  on  the  upper  sides  of  the  tube.  The  spirit  to  be 
tested  is  first  diluted  or  strengthened  until  it  has  a  S.G.  of  934'6 
at  15°  C. — i.e.,  contains  50  per  cent.,  by  volume,  of  real  alcohol 
— and  100  c.c.  of  this  prepared  spirit  is  carefully  run  on  to  the 
top  of  the  chloroform.  The  stopper  is  greased  with  vaseline 
and  tightly  fitted,  and  the  whole  tube  immersed  for  an  hour 
in  water  for  the  chloroform  to  settle  (which  process  is  aided  by 
occasional  tapping).  After  an  hour  the  volume  of  the  bottom 
layer  is  read  off;  if  the  spirit  is  pure,  this  volume  will  now  be 
37" I  c.c,  but  if  it  contains  i  per  cent.,  by  volume,  of  amylic 
alcohol,  the  bottom  layer  will  measure  39"i  c.c;  thus  giving 
an  increase  of  i  c.c.  for  each  J  per  cent.,  by  volume,  of  amylic 
alcohol  in  the  sample. 

When  this  process  is  applied  to  the  ordinary  raw  spirits  of 
commerce,  the  results  are  somewhat  below  the  truth,  on  account 
of  the  presence  of  other  impurities,  which  have,  however,  less 
tendency  to  pass  into  the  chloroform. 

The  commonest  form  of  adulteration  of  spirits  is  by  the  addition 
of  water.  When  the  distillate  gives  a  decided  red  colour  within 
fifteen  minutes  with  i  per  cent,  nitro  -  prusside  of  sodium 
solution  and  ammonia,  methylated  spirit  is  present.  The  tests 
of  taste  and  odour  alone  afford  an  excellent  index  to  purity. 

Whisky,  like  brandy,  is  frequently  coloured  with  caramel. 

Gin  is  comparatively  free  from  fusel  oil.  It  is  made  from 
cereals,  and  flavoured  with  juniper  berries,  etc. 

Rum  is  generally  obtained  by  distilling  fermented  molasses. 

Wine. 

Wine  is  the  fermented  juice  of  the  grape.  The  amount  of 
alcohol  depends  on  the  amount  of  glucose  present  in  the  grape- 
juice.  One  molecule  of  glucose  forms  two  of  alcohol  and  two 
of  carbonic  acid  (CgHi20g=2C2HgO  +  2C02)- 

The  different  kinds  of  wine,  and  even  the  different  makes  of 
the  same  wine,  vary  considerably  in  their  composition.  The 
alcohol  generally  constitutes  from  8  to  18  per  cent,  by  weight,  the 
solid  residue  from  2  to  6  per  cent.,  and  the  mineral  ash  consti- 
tutes about  0-2  per  cent.  Mineral  ash  below  0-15  per  cent,  would 
justify  suspicion. 


326  LABORATORY   WORK 

The  estimation  of  the  acidity  is  of  importance.  In  wine  the 
acidity  is  generally  returned  in  terms  of  crystallized  tartaric  acid 
Per  cent.  The  sample  should  be  diluted  before  titration,  well 
shaken  to  remove  any  CO2  present,  and  phenolphthalein  used  as 
indicator.  Every  c.c.  of  the  decinormal  soda  required  for 
neutralization  =7-5  milligrammes  of  cr3^stallized  tartaric  acid. 
The  acidity — which  is  chiefly  due  to  such  acids  as  tartaric,  malic, 
acetic,  formic  and  butyric — should  not  exceed  i'2  per  cent,  of 
tartaric  acid.  It  very  rarely  exceeds  0'8  in  genuine  samples, 
and  is  seldom  below  0-4.  About  |  of  the  total  acidity  in  white 
wines  and  not  less  than  \  in  red  wines  should  be  due  to  volatile 
acids.  The  volatile  acids  may  be  estimated  as  follows  (Win- 
disch) :  The  total  acidity  in  25  c.c.  of  the  wine  is  estimated  as 
tartaric  acid;  25  c.c.  of  the  wine  are  then  evaporated  in  a  china 
basin  to  a  volume  of  2  to  3  c.c,  25  c.c.  of  hot  water  are  added, 
and  the  whole  again  evaporated  down  to  3  c.c. ;  another  25  c.c. 
of  water  are  added,  and  after  evaporation  the  residue  is  dissolved 
in  hot  water,  and  the  solution  titrated.  The  result,  calculated 
into  tartaric  acid,  is  the  non-volatile  acidity.  The  difference 
between  this  and  the  total  acidity  gives  the  volatile  acidity  as 

FIG.    69. TORULA    CEREVISIiE    (YEAST    PLANT).       ( X  ABOUT    200.) 

tartaric  acid.  The  tartaric  acid  is  converted  to  acetic  acid  by 
multiplying  by  0-8  (since  tartaric  acid  is  to  acetic  acid  as  7*5  is 
to  6-o),  for  the  volatile  acidity  is  always  expressed  as  acetic 
acid. 

The  commoner  adulterants  are  water,  sugar,  various  ethers, 
logwood,  sulphate  of  lime  and  alum;  and  these  are,  of  course, 
especially  employed  in  the  manufacture  of  the  cheaper  wines. 
Calcium  sulphate  is  used  to  improve  the  appearance  of  wines 
by  clarifying  and  furnishing  a  brighter  and  more  permanent 
colour,  and  it  also  improves  the  keeping  qualities.  The  grapes 
are  sprinkled  with  sulphate  of  lime  either  before  or  after  they  are 
put  into  the  vat.  This  so-called  "  plastering  "  may  be  injurious 
to  health;  it  is  indicated  when  the  SO3  in  100  c.c  exceeds  0-092 


WINE  327 

gramme;  it  gives  rise  to  the  formation  of  potassium  sulphate, 
which  has  a  decided  purgative  action.  In  Fr<-mcc  this  salt  is 
not  permitted  to  exceed  0-2  per  cent.  If  50  c.c.  of  tlie  wine  are 
acidified  with  HCl  and  precipitated  hot  with  barium  chloride, 
the  sulphate  found  may  be  calculated  as  potassium  sulphate. 
Sodium  chloride  is  sometimes  added;  it  should  not  exceed  0-05 
per  cent.  The  ash  of  genuine  wines  falls  between  0'i5  and  0-35 
per  cent. 

Astringent  agents  commonly  employed  are  tannin,  alum,  and 
catechu. 

Boric  acid  and  salicylic  acids  are  often  added;  they  may  be 
normal  constituents  of  wine,  in  minute  quantities.  Fluorine 
and  saccharine  may  also  be  added  to  improve  the  keeping  qualities 
of  wine. 

Already  methods  have  been  given  by  which  most  of  the  adul- 
terants mentioned  maybe  detected.  Ihe  tannin  in  a  measured 
quantity  of  wine  may  be  estimated  as  suggested  by  Kramsky: 
From  50  to  100  c.c.  of  the  wine  are  rendered  alkaline  with 
ammonia  and  precipitated  with  a  solution  of  zinc  hydroxide. 
The  zinc  reagent  is  prepared  by  dissolving  25  grammes  of  zinc 
sulphate  in  water,  adding  sufficient  ammonia  to  redissolve  the 
precipitate  formed,  then  300  c.c.  of  ammonia,  and  finally  water  to 
make  the  volume  up  to  i  litre.  The  precipitate  of  zinc  tannate 
is  stirred  until  it  coagulates  and  settles.  Three  hundred  c.c.  of 
hot  water  are  added,  and  the  precipitate  is  collected  on  a  weighed 
filter,  washed  with  dilute  ammonia,  dried  at  100°  C,  and  weighed. 
The  filter  and  precipitate  are  now  ignited,  and  the  weight  of  zinc 
oxide  obtained  is  subtracted  from  the  total  weight,  the  difference 
giving  the  amount  of  tannin.  Gallic  acid  is  not  precipitated  by 
the  above  reagent,  and  the  ordinary  constituents  of  wine  have  no 
influence  on  the  estimation.  In  genuine  samples  of  red  wine  the 
tannin  does  not  exceed  0-25  per  cent.,  and  it  is  less  in  white  wines- 

The  colouring  agents  which  have  been  employed  are  logwood, 
blackberry,  elderberry,  and  prune  juices;  sandalwood,  cochineal, 
magenta,  Brazil  wood,  aniline  reds  and  violets,  and  indigo;  they 
are  practically  harmless;  some  of  these  colours  are  heightened 
in  tone  by  tartaric  acid. 

For  analytical  purposes  "  white  "  and  "  red  "  wines  may  be 
almost  decolorized  with  animal  charcoal,  and  "  red  "  wines  with 
basic  acetate  of  lead  and  magnesium  sulphate. 

To  estimate  sugar  (glucose),  boil  off  the  alcohol  from  200  c.c. 


328  LABORATORY  WORK 

of  the  wine:  precipitate  tlie  colouring  matter  by  lead  acetate; 
filter,  and  remove  the  lead  by  addition  of  di-sodium  phosphate; 
again  filter  and  make  up  to  200  c.c.  with  distilled  water.  Ihen 
estimate  the  sugar  by  Fehling's  method. 

Many  tests  have  been  suggested  for  the  detection  of  foreign 
colouring  matter  in  wine,  but  few  of  them  are  found  to  be  in- 
variably satisfactory  in  practice ;  two  of  the  best  are — 

(a)  A  10  per  cent,  solution  of  good  clear  gelatine  is  allowed  to 
set,  when  from  the  firm  mass  several  small  cubes  of  about  f  inch 
square  are  cut,  and  two  or  three  of  these  cubes  are  immersed 
in  the  wine  for  twenty-four  hours.  In  pure  wines  the  colouring 
matter  does  not  penetrate  the  gelatine  for  more  than  about 
1^  of  an  inch,  but  the  majority  of  the  foreign  colouring  matters 
penetrate  almost,  if  not  quite,  to  the  centre  of  the  cubes.  Dilute 
ammonia  will  dissolve  out  the  colouring  matter  of  cochineal  and 
logwood,  and  will  strike  a  blue  with  alkanet  (Dupre) . 

(&)  Fifty  c.c.  of  the  sample  are  mixed  with  i  c.c.  of  40  per  cent, 
formaldehyde  and  4  c.c.  of  hydrochloric  acid,  and  heated  for  a 
few  minutes  on  the  water-bath  until  a  precipitate  begins  to  form. 
A  slight  excess  of  ammonia  is  then  added  and  the  heating  con- 
tinued until  the  free  ammonia  has  disappeared.  Genuine  wines 
give  a  colourless  filtrate,  whilst  those  which  have  been  coloured 
artificially  retain  the  colour  of  the  dyes  (Trillat). 

The  colour  of  genuine  wine  does  not  dialyze  to  any  marked 
extent,  but  that  of  logwood,  cochineal  and  Brazil  wood  does  so 
readily. 

The  presence  of  foreign  colouring  agents  having  been  ascer- 
tained, it  remains  to  discover  their  nature  by  special  and  appro- 
priate tests.  Some  of  these  are  indicated  in  the  chapter  on 
Antiseptics  and  Colouring  Agents  in  Food. 

Wines  are  sometimes  fortified  with  inferior  brandies. 

It  may  be  necessary  to  examine  any  of  these  beverages  for 
poisonous  metals,  which  may  be  introduced  by  the  use  of  lead 
and  zinc  utensils  in  their  manufacture,  the  cleansing  of  bottles 
with  shot,  etc.  The  darkening  of  wine  which  sometimes  results 
from  the  presence  of  iron  is  not  objectionable. 

The  demand  for  white  wine  has  increased  during  recent  years, 
and  some  producers  of  red  wines  have  set  about  to  find  means  to 
convert  it  into  white.  Analyses  made  in  France  prove  that  one 
mode  of  effecting  this  is  to  treat  red  wine  with  a  mixture  of  animal 
charcoal  and  potassium  permanganate.      This  process  bleaches 


BEER  329 

the  wine,  but  at  the  same  time  leaves  a  considerable  quantity  of 
manganese  in  solution.  Wine  which  has  thus  been  treated  can 
be  recognized  by  adding  to  it  in  an  open  vessel  an  excess  of  caustic 
soda,  and  shaking.  After  a  few  minutes  a  thin  brown  layer  forms 
on  the  surface  of  the  liquid,  due  to  oxidation  by  the  air  of  the 
oxide  of  manganese  set  at  liberty  by  the  alkali. 

British  wines,  sold  as  non-alcoholic,  frequently  contain  salicylic 
acid,  and  sometimes  boric  acid. 

Beer. 

This  beverage  was  formerly  made  from  malt  and  hops  only; 
now  it  can  be  legally  made  from  starch  and  sugar  and  various 
vegetable  bitters. 

From  the  malt  the  beer  derives  maltose,  dextrine,  albuminoids 
and  salts,  and  from  the  hops  a  bitter  principle,  resin  and  tannin ; 
alcohol,  carbonic  acid,  a  little  glycerine  and  succinic  acid  are 
produced  by  the  fermentation,  and  a  small  amount  of  lactic  and 
acetic  acid  result  from  schizomycetic  fermentation. 

Pure  beer  is  the  fermented  liquor  obtained  from  the  germinating 
grain  of  barley.  The  grains  are  made  to  partially  germinate  by 
being  first  moistened  and  then  kept  warm  until  they  begin  to 
sprout.  A  small  quantity  of  the  ferment  "  diastase  "  is  thus 
produced,  and  the  diastase  acts  upon  the  starch  and  largely 
converts  it  into  the  sugar  "  maltose,"  which  is  easily  fermentable. 
Further  fermentation  is  then  prevented  by  heating  the  barley 
in  kilns.  The  malt  is  next  subjected  to  "  mashing  "  by  mixing 
with  water  at  82°  C.  and  well  crushing  and  stirring  for  about 
two  hours.  After  clarifying,  the  infusion  is  boiled  with  hops, 
and  the  cooled  liquor  or  "  wort  "  is  transferred  to  vats  to  fer- 
ment, yeast  being  added.  When  the  alcoholic  fermentation  has 
proceeded  far  enough,  the  yeast  is  removed  and  the  beer  is  run 
into  casks. 

In  recent  years  glucoses  and  invert  sugars  obtained  from  rice 
and  other  starches  by  the  action  of  dilute  sulphuric  acid  have 
been  largely  substituted  for  the  malt.  The  commercial  sulphuric 
acid  employed  is  liable  to  contain  arsenic  (derived  from  the 
iron  pyrites  used  in  its  manufacture) ;  and  this  circumstance  was 
responsible  for  a  considerable  outbreak  of  arsenical  poisoning 
among  beer  consumers,  chiefly  in  the  north-w^estern  part  of 
England,    in   the   winter    of    1900-1901.     Amounts   of   arsenic 


330  LABORATORY   WORK 

varying  from  ^^jj  to  i  grain  per  gallon  of  beer  were  discovered, 
and  some  invert  sugars  were  found  to  contain  arsenic  equivalent 
to  2" 04  grains  of  arsenious  oxide  per  pound. 

With  regard  to  the  "  finings,"  which  are  added  to  clarify  beer 
or  wine,  their  nature  is  varying,  but  they  generally  contain 
isinglass. 

Sulphites  or  bisulphites,  and  carbonates  or  bicarbonates  of  soda 
and  potash,  sulphurous,  boric,  and  salicylic  acids  and  saccharin, 
are  employed,  principally  to  check  fermentation  and  to  clarify. 
The  use  of  sulphites  has  increased  of  late  years,  while  that  of 
salicylic  acid  has  decreased.     Fluorine  may  also  be  employed. 

An  undue  amount  of  common  salt  may  be  present.  Before  it 
can  be  decided  that  salt  has  been  added,  allowance  must  be  made 
for  the  salt  in  the  brewing  water,  and  for  the  chlorides  natural 
to  the  malt  and  hops.  Fifty  grains  of  salt  per  gallon  would  be 
a  most  generous  limit  to  allow  on  these  accounts,  but  where 
possible  the  chlorine  in  the  actual  water  used  in  the  brewing 
should  be  estimated. 

Sulphurous  acid  may  find  its  way  into  beer  (and  wine)  from 
the  practice  of  sulphuring  the  insides  of  the  casks,  and  washing 
them  with  a  solution  of  calcium  bisulphite  or  sulphite  of  potas- 
sium; but  it  is  also  added  to  regulate  fermentation  and  to  produce 
a  flavour  of  age.  It  may  be  detected  by  adding  to  some  of 
the  beer  or  wine  HCl  and  zinc  powder,  and  then  laying  a  lead 
paper  over  the  mouth  of  the  bottle;  the  paper  darkens  if  sul- 
phurous acid  is  present  (S02  +  3H2=  SH2  +  2H2O). 

Alkaline  salts  are  added  to  correct  undue  acidity.  Sodium 
bicarbonate  has  also  been  employed  to  increase  the  effervescing 
property  of  the  beverage. 

Other  bitters  (quassia,  catechu,  and  tannin)  are  sometimes 
used  as  substitutes  for  hops ;  but  this  substitution  has  no  public 
health  import.  Noxious  bitters  have  in  fonner  times  been 
detected,  such  as  picrotoxine,  nux  vomica  (strychnine)  and 
picric  acid. 

The  hop  bitters  are  precipitated  by  neutral  acetate  of  lead. 
If,  therefore,  a  litre  of  beer  is  evaporated  to  about  300  c.c.  and 
then  precipitated  while  hot  with  a  solution  of  neutral  lead 
acetate,  and  the  solution  filtered  and  evaporated  to  50  c.c,  it 
has  no  bitter  taste;  whereas  if  hop  substitutes  have  been  em- 
ployed the  solution  is  distinctly  bitter. 

The  acidity  of  beer  is  an  important  consideration,  since  excess 


BEER  331 

either  denotes  commencing  changes  of  a  deteriorating  character, 
or  imphes  the  addition  of  sulphuric  acid  (employed  to  clarify,  to 
lighten  the  colour,  and  to  give  the  beer  the  hard  taste  which 
naturally  only  comes  by  age).  The  normal  acidity  of  beer 
depends  upon  the  presence  of  carbonic,  acetic,  lactic,  malic, 
tannic,  and  gallic  acids,  and  it  can  be  estimated  in  terms  of 
glacial  acetic  acid  by  neutralization  with  decinormal  soda  solu- 
tion (i  c.c.  of  which=6  milligrammes  of  glacial  acetic  acid). 
The  acidity  of  100  c.c.  of  beer  should  not  exceed  30  c.c,  of  deci- 
normal alkali. 

The  ash  should  not  be  less  than  0-12  nor  more  than  0-40 
gramme  per  100  cc;  if  the  latter  figure  is  exceeded,  probably 
some  mineral  adulterant  has  been  added, 

A  neutral  solution  of  lead  acetate  will  largely  decolorize  beer. 
Herb  and  botanic  beer  and  ginger  beer,  which  are  sold  as 
"  non-alcoholic  "  beverages,  often  contain  proof -spirit  in  excess 
of  the  limit  of  2  per  cent,  A  few  of  the  many  samples  of  ginger 
beer  analyzed  at  the  Government  laboratories  during  the  years 
1905,  1906,  and  1907  contained  6  per  cent,  of  proof-spirit — one 
sample  containing  9-5  per  cent,;  a  sample  of  herb  beer  contained 
10-5  per  cent,  of  proof -spirit,  and  one  of  dandelion  stout  12-3  per 
cent. 


CHAPTER  X 

vinegar— lime  and  lemon  juice— mustard— pepper 
—sugar— honey 

Vinegar  (Acetic  Acid). 

This  is  the  acid  liquid  obtained  from  the  acetous  fermentation  of 
various  decoctions  or  fruit  juices.  Wine,  cider,  and  malt  vinegars 
are  due  to  the  oxidation  of  alcohol  by  the  action  of  Mycodcrma 
aceti.  The  bulk  of  the  vinegar  used  in  this  country  is  derived 
from  malt  and  barley,  in  France  from  wine,  and  in  the  United 
States  from  cider.  Spirit  vinegar  is  made  in  Germany,  and  small 
quantities  reach  this  country. 

Vinegar  is  essentially  dilute  acetic  acid,  generally  4  to  5  per 
cent.,  along  with  a  little  acetic  ether.  Vinegars  made  chiefly 
from  unmalted  barley,  maize,  rice,  and  other  grains,  and  from 
sugar  or  molasses,  are  sometimes  sold  as  malt  vinegar.  Pyro- 
ligneous  acid  (wood  acid)  has  been  employed  to  make  up  vinegar; 
it  is  derived  from  the  destructive  distillation  of  wood,  and  often 
a  little  caramel  is  added  to  make  it  resemble  malt  vinegar. 

In  this  country  there  are  no  legal  standards  relating  to  vinegar, 
but  "  a  pure  malt  vinegar  "  should  contain  nothing  but  what  is 
furnished  to  it  by  the  barley,  the  yeast,  and  the  water  which  are 
used  in  its  manufacture. 

The  Local  Government  Board  is  of  opinion  that  the  following 
definitions  may  properly  be  adopted : 

Vinegar  is  a  liquid  derived  wholly  from  alcoholic  and  acetous 
fermentations.  It  shall  contain  not  less  than  4  grammes  of 
acetic  acid  (CH3COOH)  in  100  c.c.  of  vinegar;  it  shall  not  con- 
tain arsenic  in  amounts  exceeding  0-0143  milligramme  per  100  c.c. 
of  vinegar,  nor  any  sulphuric  or  other  mineral  acid,  lead,  or 
copper,  nor  shall  it  contain  any  foreign  substance  or  colouring 
matter  except  caramel. 

332 


VINEGAR  333 

Malt  vinegar  is  derived  wholly  from  malted  barley  or  wholly 
from  cereals  the  starch  of  which  has  been  saccharified  by  the 
diastase  of  malt. 

Artificial  vinegar  is  any  vinegar  or  substitute  for  vinegar 
containing,  or  derived  from  any  preparation  containing,  any 
added  acetic  acid  which  is  not  wholly  the  product  of  alcoholic 
and  subsequent  acetous  fermentation.  It  shall  contain  not  less 
than  4  grammes  of  acetic  acid  (CH3COOH)  in  100  c.c.  of  the 
artificial  vinegar.  It  shall  not  contain  arsenic  in  amounts  ex- 
ceeding 0-0143  milligramme  per  100  c.c.  of  artificial  vinegar, 
nor  any  sulphuric  or  other  mineral  acid,  lead,  or  copper,  nor 
shall  it  contain  any  foreign  substance  or  colouring  matter  except 
caramel. 

The  practice  of  adding  mineral  acid  to  brewed  vinegar  is  said 
to  have  ceased;  but  free  sulphuric  acid  is  sometimes  added  to 
cheap  vinegars,  made  by  the  addition  of  acetic  acid  to  water. 

Free  sulphuric  acid  may  be  detected  by  Ashby's  test:  Dry  a 
drop  of  the  aqueous  extract  of  logwood  (0-5  gramme  to  100  c.c. 
of  boiling  water,  and  allowed  to  stand  for  a  few  hours)  on  a 
porcelain  plate,  add  a  drop  of  the  vinegar,  and  again  dry.  Pure 
vinegar  gives  a  yellow  residue,  but  if  free  mineral  acid  is  present 
the  residue  is  red. 

Mineral  acids  may  also  be  detected  by  adding  4  to  5  drops  of 
a  o-i  per  1,000  solution  of  methyl  violet;  pure  acetic  acid  vinegar 
shows  no  change  of  colour,  but  traces  of  free  mineral  acid  cause 
the  violet  colour  to  change  to  a  bluish-green  or  green. 

To  estimate  the  quantity  of  sulphuric  acid  present,  mix  50  c.c. 
of  the  vinegar  with  25  c.c.  ^o  NaHO  in  a  platinum  dish,  evaporate 
to  dryness,  and  ignite  at  a  low  heat.  Add  25  c.c.  —^  HCl  to 
neutralize,  heat  to  expel  COg,  and  filter.  Wash  out  with  hot 
water,  adding  washings  to  filtrate.  Estimate  free  acid  present 
with  /o  NaOH,  using  phenolphthalein  as  the  indicator.  The 
number  of  c.c.  used  x  0-0049=  amount  ^^  ^^^^  H2SO4  in  50  c.c. 
of  the  sample  (Otto  Hehner).  Some  allowance  must  be  made 
for  the  sulphates  in  the  water  used  in  the  manufacture  of  the 
vinegar. 

If  the  ash  of  vinegar  is  alkaline  (from  the  conversion  of  the 
organic  salts  into  carbonates  by  the  ignition),  this  shows  that 
no  free  sulphuric  acid  was  present. 

The  amount  of  sulphuric  acid  can  be  estimated,  as  in  water, 
by  precipitating  as  barium  sulphate.    The  precipitate  is  then 


334  LABORATORY   WORK 

collected,  washed,  dried,  ignited,  and  weighed,  and  the  weight 
multiplied  by  0-343  gives  the  weight  of  SO3. 

The  acidity  of  vinegar  should  not  fall  below  4  to  5  per  cent,  of 
glacial  acetic  acid  (C2H4O2),  and  the  specific  gravity  does  not 
fall  below  1015  in  good  vinegar.  In  artificial  vinegars  made  by 
diluting  acetic  acid  the  specific  gravity  is  generally  about  1007, 
and  the  mineral  ash  only  about  0035  (as  against  0-35  in  brewed 
vinegars) . 

To  estimate  the  total  acidity  of  vinegar,  take  10  c.c,  dilute  it 
with  90  c.c.  of  distilled  water,  and  into  10  c.c.  of  the  mixture 
(which  contains  i  c.c.  of  vinegar)  run  decinonual  soda  solution 
until  the  neutral  stage  is  reached,  using  phenolphthalein  as 
indicator.  The  number  of  c.c.  of  soda  solution  required 
X  o-oo6  X  100=  the  percentage  amount  of  acetic  acid  present. 

Potassium  ferrocyanide  has  been  used  to  clarify,  and  a  little 
hydrocyanic  acid  results.  This  enters  into  unstable  combination 
with  the  organic  constituents,  and  although  no  ill -effects  to 
consumers  have  been  observed  the  practice  is  objectionable. 

The  preservative  now  chiefly  employed  is  calcium  bisulphite, 
which  may  be  added  to  the  finished  vinegar,  or  may  gain  access 
to  the  vinegar  from  its  use  for  cleansing  vessels.  Salicylic  acid 
and  boric  acid  are  also  sometimes  employed. 

In  cases  where  vinegar  has  been  added  to  "  tinned  "  articles 
(pickles,  fish,  etc.),  the  liquid  should  be  tested  for  metals,  since 
the  vinegar  adds  considerably  to  the  solvent  action  of  the  juices. 
Copper  may  gain  access  from  apparatus  employed  in  the  making 
of  vinegar;  but  metallic  pumps  and  pipes  are  now  generally 
superseded  by  ebonite.  Traces  of  arsenic  may  also  be  found 
when  arsenical  malt  has  been  employed. 

The  detection  of  heavy  metals  is  difficult  in  the  case  of  highly 
coloured  vinegars.  The  following  method  is  recommended  for 
lead  and  copper:  i  c.c.  of  concentrated  hydrochloric  acid  is 
added  to  10  c.c.  of  the  boiling  vinegar,  and  the  liquid  treated 
little  by  little  with  potassium  chlorate  until  of  a  pale  yellow 
colour,  after  which  it  is  boiled  for  a  minute,  treated  with  sodium 
acetate,  and  subjected  to  a  current  of  H2S. 
Vinegar  eels  {Anguillula  oxyphila)  are  not  considered  injurious. 


LIME-JUICE   AND    LEMON-JUICE  335 


Lime-juice  and  Lemon-juice. 

Lime-juice  is  the  juice  of  Citrus  limeita  fortified  with  about 
I  ounce  of  brandy  to  every  10  ounces  of  juice.  The  specific 
gravity  (at  15°  C.)  is  generally  about  1037,  the  alcohol  forms 
about  4  per  cent.,  and  the  calculated  free  citric  acid  is  about 
30  grains  to  the  ounce  (i  c.c.  of  decinormal  soda  solution  =  6-9 
milligrammes  of  citric  acid.  The  percentage  amount  of  acid 
X  4*375  gives  grains  per  ounce) . 

The  ash  of  lime-juice  dissolved  in  neutral  distilled  water  is 
alkaline  in  reaction. 

Adulteration. — The  juice  may  be  entirely  made  up  of  citric 
acid  flavoured  with  essence  of  lemon;  or  of  citrate  of  potash, 
tartrates,  the  juices  of  plants,  etc.  Sulphiuic  acid  is  sometimes 
added,  and  also  water.  The  usual  determinations  made  are: 
the  acidity,  the  alkahnity  of  the  ash,  the  fragrancy  of  the  extract, 
the  physical  characters  (agreeable  odour  and  taste,  amber  colour, 
and  clearness),  and  the  freedom  from  sulphuric  and  tartaric 
acids. 

To  test  for  tartaric  acid,  take  2  grammes  of  the  lime-juice, 
and  dissolve  in  45  c.c.  of  proof -spirit  (methyl  spirit  diluted  to  a 
density  of  920).  Then  add  5  c.c.  of  a  cold  saturated  solution 
of  potassium  acetate  in  proof-spirit,  and  stir  for  ten  minutes, 
when  a  crystalline  precipitate  of  the  acid  tartrate  of  potassium 
forms.  If  the  precipitate  is  small  in  amount,  only  white  streaks 
may  be  observed  on  the  side  of  the  vessel  in  the  track  of  the  glass 
stirring-rod. 

In  estimating  acidity,  it  is  necessary  to  first  considerably 
dilute  the  juice. 

Lemon-juice,  according  to  the  British  Pharmacopoeia,  should 
have  a  specific  gravity  of  1030  to  1040,  should  contain  30  to  40 
grains  of  free  citric  acid  per  ounce,  and  should  not  yield  more 
than  3  per  cent,  of  ash.  The  B.P.  figure  for  citric  acid  is  too 
high.  The  Board  of  Trade  standard  is  a  specific  gravity  (without 
spirit)  of  not  less  than  1030,  and  an  acidity  equal  to  30  grains 
per  ounce  of  citric  acid. 

These  juices  should  be  tested  for  salicylic  acid,  sulphites,  and 
boric  acid. 


33^  LABORATORY   WORK 


Mustard. 

The  mustard  in  general  use  is  practically  a  mixture  of  brown 
and  white  mustard-seed  ground  to  flour. 

None  of  the  adulterants  employed  are  of  a  harmful  nature. 
They  are:  Turmeric  and  aniline  yellow,  wheat  starch,  and  when 
much  foreign  material  is  added,  aniline  dye  and  a  little  cayenne 
pepper  may  be  employed.  The  brownish-red  reaction  of  tur- 
meric with  ammonia,  and  the  bluing  of  starch  in  the  presence 
of  iodine  after  boiling  some  of  the  sample  with  distilled  water 
and  allowing  to  cool,  are  chemical  tests  of  service,  for  pure 
mustard  contains  no  starch  or  turmeric. 

Mustard  oil  is  sometimes  abstracted. 

Wliite  mustard  under  the  microscope  presents  certain  well- 
marked  characteristics.  The  outer  coat,  or  cuticle,  consists  of 
a  layer  of  large  hexagonal  (so-called  "  infundibuliform  ")  cells, 


FIG.    70. THE    CUTICLE    OF    THE    WHITE    MUSTARD-SEED.       (X200.) 

which  present  a  central  ostium  occupied  by  other  bodies,  called 
mucilage  cells.  When  water  is  added  these  latter  swell  up,  and 
escape  from  the  mouth  of  the  large  hexagonal  cells  into  the 
water,  to  which  they  appear  to  furnish  mucilage. 

Inside  this  layer  are  three  less  characteristic  ones,  the  inner- 
most consisting  of  a  thin  layer  of  large  granular  cells;  and  the 
interior  of  the  seed  comprises  a  fairly  regular  areolar  network, 
containing  granular  matter  and  minute  oil  globules. 

Mustard  polarizes  well. 

Pepper. 

White  pepper  is  obtained  from  the  pepper  berry  after  the  dark 
outer  layer  of  pericarp  has  been  removed.  This  accounts  for  the 
difference  in  the  composition  of  black  and  white  peppers. 

Pepper  is  considerably  adulterated,  but  mostly  with  agents 


PEPPER 


337 


which  are  harmless:  Various  starches  (rice  chiefly)  and  the 
ground  stones  from  olives  ("  poivrette  ")  have  been  employed. 

Any  added  mineral  matter  could,  as  in  flour,  be  mostly 
separated  by  shaking  up  thoroughly  with  chloroform.  A  little 
sand  or  earthy  matter  is  general,  owing  to  the  fact  that  the 
berries  are  allowed  to  dry  on  earthen  surfaces,  when  many  of 
their  minute  furrows  become  filled  with  the  earth;  and  by  the 
wearing  of  the  stones  between  which  the  berries  are  ground  the 
powder  may  also  acquire  a  trace  of  sand.  A  very  small  allowance 
has  to  be  made  for  the  presence  of  this  unavoidable  mineral  matter. 

A  large  proportion  of  the  pepper  sold  has  been  reduced  in 
quality  by  being  bleached. 


FIG.  71 


A,  Isolated  starch  grains;  B,  cells  of  the  perisperm  with  starch; 
C,  schlerenchymatous  cells. 


A  rather  rough  but  serviceable  test,  recommended  by  Neuss, 
consists  in  covering  the  pepper  with  concentrated  hydrochloric 
acid ;  when,  if  the  sample  is  pure  pepper,  it  becomes  of  an  intense 
and  uniform  yellow,  while  most  of  the  foreign  ingredients  remain 
uncoloured.  The  microscope  furnishes  a  useful  means  of  detect- 
ing adulteration. 

The  ash  of  black  pepper  averages  from  3  to  5  per  cent.;  that 
from  white  pepper  i  to  3  per  cent. 

According  to  the  resolution  of  Bavarian  chemists  (i8go),  the 
limits  of  ash  should  be : 

For  black  pepper,  6-5  per  cent.  (2  per  cent,  insoluble  in  HCl); 
for  white  pepper,  3-5  per  cent,  (i  per  cent,  insoluble  in  HCl). 

Unlike  mustard,  pepper  contains  starch;  but  this  is  not  the 
case  with  "  poivrette." 

Microscopical  Characters  of  Pepper. — A  transverse  section  of 
the   black  -  pepper   berry   shows   the  following  notable   points : 


338  LABORATORY   WORK 

Starting  from  the  cortex,  most  externally  is  a  layer,  two  or 
three  cells  deep,  arranged  vertically,  and  very  much  resembling 
bean-starch  granules  in  appearance — i.e.,  ovoid  in  shape,  with  a 
central  linear  hilum  crossed  by  transverse  markings;  next  follows 
an  ill-defined  layer  of  elongated  cells  arranged  transversely  to 
the  foregoing,  and  then  a  sort  of  irregular  reticular  tissue  con- 
taining oil  globules;  more  internally  still,  a  well-defined  single 
layer  of  large  vertical  more  or  less  flask-shaped  cells  is  seen. 
The  rest  of  the  interior  of  the  berry  consists  of  flattened  angular 
cells,  dovetailed  into  each  other. 

The  following  is  a  chemical  test  for  "  poivrette  ":  Digest  for 
forty-eight  hours  i  gramme  of  phloroglucol  in  50  c.c.  of  hydro- 
chloric acid  (S.G.  i-i),  and  then  decant  the  clear  solution. 
Just  cover  some  of  the  pepper  with  this  reagent,  and  heat 
cautiously  until  fumes  of  hydrochloric  acid  begin  to  come  away. 
"  Poivrette  "  furnishes  a  deep  cherry -red  colour,  but  pepper  a 
yellow  or  faint  brown . 

"  Long  pepper  "  is  very  inferior  in  strength  to  other  kinds. 
It  consists  of  the  fruit  of  Chavica  Roxhurghii,  and  it  usually  con- 
tains a  considerable  quantity  of  extraneous  mineral  matter  (clay 
and  soil).     It  may  be  used  to  adulterate  pepper. 

By  polarized  light  an  entirely  dark  field  may  be  obtained  with 
pure  pepper  on  rotating  the  prisms,  but  this  is  not  possible  when 
"  poivrette,"  "  long  pepper,"  or  rice  are  present. 

Cayenne  pepper  has  been  adulterated  with  oxide  of  iron,  brick- 
dust,  rice  starch,  etc.  The  mineral  ash  should  not  exceed  6-5 
per  cent.,  and  not  more  than  0*5  per  cent,  of  the  ash  should  be 
insoluble  in  HCl. 

Other  Spices. 

Ginger  is  sometimes  adulterated  with  "  exhausted  "  ginger 
which  has  been  used  in  the  manufacture  of  ginger  beer  or  ginger 
wine.  The  soluble  ash  should  be  at  least  1-5  per  cent.  Cara- 
ways and  cloves  which  have  had  the  essential  oil  extracted  from 
them  may  be  mixed  with  the  pure  commodity ;  and  ground  mixed 
spices  may  be  adulterated  with  damaged  macaroni  and  vermicelli, 
or  walnut  shells,  olive  stones,  etc.,  ground  up  into  a  powder. 

Sugar. 

The  sugar  of  commerce  is  almost  entirely  beet  and  cane 
sugar  (C12H22O11),  for  very  little  glucose  comes  into  ordinary 
domestic    employ ;    but    sometimes    beet  -  sugar    is    artificially 


SUGAR  339 

coloured  with  minute  quantities  of  aniline  colours,  and  thus 
made  to  resemble  cane-sugar. 

The  colouring  matter  foreign  to  sugar  may  generally  be 
detected  by  washing  about  lOO  grammes  of  the  sugar  in  a  flask 
with  alcohol  (90  per  cent.).  If  the  dye  is  not  removed,  the 
washing  must  be  repeated  until  it  is.  The  solution  is  then 
filtered,  evaporated  to  dryness,  and  again  taken  up  in  a  little 
alcohol.  A  skein  of  wool  slightly  mordanted  with  aluminium 
acetate  is  placed  in  the  solution,  which  is  warmed  over  the 
water-bath.  The  skein  is  removed  after  a  while,  washed  with 
water  and  dried,  when  it  retains  a  permanent  yellow  dye.  The 
colour  natural  to  sugar  will  not  furnish  a  solution  which  is 
capable  of  permanently  dyeing  wool. 

Demerara  sugar  owes  its  bright  tint  to  the  natural  colouring 
matter  of  the  cane  being  fixed  on  the  sugar  by  means  of    a 


FIG,  72. THE  SUGAR  MITE  (aCARUS  SACCHARI).   (MAGNIFIED.) 

mordant  of  chloride  of  tin.  To  imitate  this,  beet-sugar  crystals 
are  sometimes  stained  with  an  aniline  dye.  This  can  often  be 
detected  by  merely  moistening  the  sugar  with  a  little  strong 
hydrochloric  acid,  which  turns  the  yellow  dye  to  a  bright  pink, 
but  does  not  affect  the  natural  colour. 

Ultramarine  blue  is  sometimes  added  to  granulated  and  loaf 
sugars  to  improve  their  colour.  The  sample  should  be  dissolved 
in  water,  and  the  colouring  matter  allowed  to  settle,  when  it  can 
be  collected  and  washed  with  water.  HCl  discharges  this  colour 
and  liberates  sulphuretted  hydrogen. 

In  estimating  the  ash  of  sugar  it  is  best  to  carefully  ignite 
5  grammes  of  the  powdered  sugar,  after  mixing  (by  means  of  a 
glass  rod)  with  5  to  7  grammes  of  coarsely  powdered  quartz  sand 
(previously  ignited  and  weighed) .  The  platinum  dish  may,  how- 
ever, be  perceptibly  injured  in  the  process.  The  ash  of  genuine 
sugar  does  not  exceed  2  per  cent.     Carbonate  of  calcium  may  be 


340  LABORATORY   WORK 

found,  as  it  is  said  to  be  used  in  the  whitening  of  sugar  (A.  Hill). 
Any  insoluble  mineral  adulteration  would  be  detected  by  dis- 
soh'ing  the  sugar  in  water  and  then  filtering. 

The  amount  of  sugar  present  in  any  substance  is  best  estimated 
by  Fehling's  method,  the  rationale  of  which  is  as  follows:  If 
solutions  of  caustic  potash  and  sulphate  of  copper  be  boiled 
together  the  mixture  becomes  black,  owing  to  the  formation  of 
the  black  oxide  of  copper.  The  presence  of  certain  organic 
substances,  however,  and  amongst  them  grape-sugar,  prevents 
the  copper  becoming  so  highly  oxidized,  and  the  reddish-brown 
sub-oxide  of  copper  is  in  consequence  formed.  Cane,  beet,  and 
maple  sugar  (C12H22O11)  have  no  such  action,  but  by  heating 
the  clarified  syrup  (containing  not  more  than  25  grammes  of  the 
solid  per  100  c.c.)  in  a  water-bath  along  with  about  one-tenth  of 
its  bulk  of  strong  HCl  for  fifteen  minutes,  it  is  readily  inverted 
into  glucose  (C6H12O6).  Before,  however,  the  inverted  sugar  is 
estimated  by  Fehling's  method,  the  acid  solution  must  be 
neutralized. 

By  inversion,  then,  is  understood  the  conversion  of  non- 
reducing  carbohydrates  into  sugars  of  the  formula  CeHjo^^e, 
which  directl}'  reduce  Fehling's  solution  to  a  reddish-brown 
sub-oxide  of  copper. 

Levulose  (C6Hi20g)  or  fruit-sugar,  maltose  (C12H22O11)  or  malt- 
sugar,  and  lactose  (C12H22O11)  or  milk-sugar,  reduce  Fehling's 
solution  at  once. 

Fehling's  solution  is  made  b}-  dissolving  34-64  grammes  of 
pure  cupric  sulphate  in  water  and  diluting  to  500  c.c.  The 
solution  so  obtained  is  mixed  with  another  solution  prepared 
by  dissolving  173  grammes  of  sodio-potassic  tartrate  in  water, 
adding  100  c.c.  of  sodic  hydrate  solution  (S.G.  1-34),  and  diluting 
the  mixture  to  500  c.c.  When  these  two  solutions  (each  of 
500  c.c.)  are  united,  we  obtain  i  litre  of  ordinary  Fehling's  solution. 

The  solution  should  be  preserved  in  small,  well-stoppered 
bottles  kept  full  and  in  the  dark. 

The  estimation  of  sugar  by  Fehling's  method  is  performed  as 
follows : 

Take  50  c.c.  of  Fehling's  solution,  bring  to  the  boil  in  a  por- 
celain dish,  and  then  run  in  that  amount  of  very  dilute  (about 
r  per  cent.)  sugar  solution,  which,  when  boiled  for  two  minutes, 
decolorizes  the  Fehling's  solution.  Then  filter  the  hot  solution. 
If  the  filtrate  is  bluish-green,  far  too  little  sugar  has  been  added ; 


SUGAR  341 

if  it  is  greenish,  barely  sufficient  sugar  has  been  added ;  if  yellow, 
either  the  right  quantity  or  too  much  sugar  has  been  added.  In 
the  case  of  the  filtrate  being  yellow  a  little  copper  may  still  (ixist 
in  solution.  To  detect  this,  acidify  with  acetic  acid,  and  add  a 
drop  or  two  of  potassium  ferrocyanide;  a  bronze  coloration  will 
indicate  that  barely  sufficient  sugar  has  been  added. 

Thus  by  a  series  of  experiments  the  precise  amount  of  sugar 
solution  required  to  reduce  50  c.c.  of  Fehling's  solution  is  arrived 
at.  Suppose  25  c.c.  of  the  sugar  solution  are  required.  Then 
25  c.c.  =  50  c.c.  of  Fehling's  solution  =  0-2375  gramme  of  grape- 
sugar;  for,  according  to  Soxhlet,  if  we  work  with  dilute  solutions 
contaiuing  as  near  as  possible  i  per  cent,  of  sugar,  50  c.c.  of 
Fehling's  solution  are  reduced  by — 

0*2375  gramme  of  grape-sugar. 
0-2470  ,,  invert-sugar. 

0-2572  ,,  levulose. 

0-3380  „  lactose. 

0-3890  „  maltose. 

Ling  and  Rendle's  indicator  is  a  very  useful  reagent  for  deter- 
mining the  complete  reduction  of  Fehling's  solution.  It  is  made 
as  follows:  i  gramme  of  ammonium  thiocyanate  and  a  similar 
quantity  of  ferrous  ammonium  sulphate  are  dissolved  in  10  c.c. 
of  warm  distilled  water;  then  5  c.c.  of  concentrated  hydrochloric 
acid  are  added.  This  produces  a  dark  brown  solution,  which 
must  be  decolorized  before  using.  To  effect  this  a  trace  of  zinc 
dust  is  added  to  about  2  c.c.  of  the  stock  solution. 

About  a  dozen  drops  of  the  indicator  should  be  placed  upon 
a  white  porcelain  slab,  and  drops  from  the  dish  containing  the 
boihng  Fehling's  solution  should  be  transferred  by  means  of  a 
glass  rod  to  the  drops  on  the  slab.  If  a  bright  blood-red  colour 
is  struck,  reduction  is  not  yet  complete;  otherwise,  no  colour 
results.  In  another  simple  method  (W.  F.  Sutherst)  a  drop  of 
the  mixture  is  placed  on  the  top  side  of  a  filter-paper  folded  in 
half,  the  filtrate  passes  through,  and  the  spot  is  treated  with  a 
drop  of  a  dilute  acetic  acid  solution  of  i  per  cent,  potassium 
ferrocyanide.  On  holding  up  to  the  light,  the  faintest  trace  of 
copper  ferrocyanide  is  plainly  seen,  and  the  end  of  the  reaction 
readily  indicated. 

It  is  important  to  realize  that  milk-sugar  takes  a  much  longer 
time  to  reduce  Fehling's  solution  than  glucose  does. 


342  LABORATORY   WORK 

The  use  of  glucose  in  jams,  jollies,  confectioner}',  and  marma- 
lades cheapens  these  products,  and  it  serves  to  prevent  crystal- 
lization of  cane-sugar;  hence  it  is  largely  employed,  although  it 
is  not  essential  to  the  production  of  these  preserves.  It  is  also 
employed  in  sundry  beverages,  particularly  brewed  ginger  beer 
and  certain  kinds  of  wines. 

Glucose  is  the  chief  adulterant  of  golden  syrup.  Calcium 
sulphate  is  a  common  impurity  in  commercial  glucose,  and  its 
presence  may  sometimes  be  detected  by  obtaining  a  filtered 
solution  of  the  sample  and  noting  a  distinct  turbidity  on  adding 
ammonium  oxalate. 

Honey. 

The  microscope,  by  revealing  the  absence  of  pollen  grains, 
would  give  a  certain  indication  of  any  artificicQ  comb  prepared 
from  paraffin  wax,  etc.  Beeswax  carbonizes  by  treatment  with 
boiling  strong  sulphuric  acid;  not  so  paraffin  wax.  Glucose, 
cane-sugar,  low-grade  malt  extracts,  and  different  starches  have 
been  employed  to  adulterate  honey.  Honey  containing  starch 
syrup  is  coloured  red  to  violet  by  iodine  solution;  not  so  pure 
honey. 

Honey  has  given  rise  to  poisoning  in  New  Zealand  and  else- 
where, the  poison  being  derived  from  poisonous  plants  the 
precise  nature  of  which  has  not  been  determined. 

Genuine  honey  should  not  contain  more  than  8  per  cent,  of 
cane-sugar,  25  per  cent,  of  moisture,  and  0"5  per  cent,  of  ash. 

Jams. 

Certain  jams  may  be  adulterated  with  apple-pulp  or  other 
cheaper  fruits.  For  sweetening,  starch-glucose  may  be  em- 
ployed instead  of  cane  or  beet  sugar,  and  salicylic  acid  may  be 
added  as  a  preservative.  Apple-pulp  may  be  detected  by  boil- 
ing some  of  the  jam  with  distilled  water,  allowing  to  cool,  and 
adding  iodine,  when  a  blueing  will  denote  the  addition  of  apple- 
pulp  or  some  other  adulterant  containing  starch.  In  testing  for 
preservatives,  it  should  be  known  that  traces  of  salicylic  and 
benzoic  acids  exist  normally  in  many  fruits. 


CHAPTER  XI 


COFFEE— COCOA— CHOCOLATE 

The  unground  coffee-bean,  as  it  reaches  the  market,  consists  of 
the  true  substance  of  the  bean  more  or  less  enclosed  in  a  thin 
skin,  which  is  always  most  evident  in  the  furrow.  These  coffee- 
berries  before  use  are  roasted  at  a  high  temperature  to  develop 
aroma,  flavour,  and  colour. 

Bell  gives  an  analysis  of  Mocha  coffee,  which  serves  to  show 
the  respective  amounts  of  the  constituents  of  the  raw  bean,  and 
the  changes  in  these  amounts,  which  are  brought  about  by 
roasting. 

Caffein   .  . 

Saccharine  matter 

Caffeic  acids 

Extracted      by     alcohol,     and      containin 

nitrogenous  and  colouring  matter 
Fat  and  oil 

Legumin  or  albumin    .  . 
Dextrin 
Cellulose  and  insoluble  colouring  matter 

Ash         

Moisture 


Very  generally  the  caffein,  fat,  and  moisture  are  found  to  be 
somewhat  higher  than  the  above  figures,  and  the  cellulose  lower. 

The  fat  should  amount  to  at  least  lo  per  cent.,  and  the  ash  to 
3  per  cent. 

A  hot-water  infusion  of  the  ground  coffee  contains  the  oil, 
sugar,  caffein,  most  of  the  mineral  matters,  dextrin,  and  some 
of  the  albuminous  matters. 

A  dulteration. — Chief  among  the  adulterants  is  chicory,  which 
is  prepared  from  the  root  of  the  wild  endive. 

The  admixture  of  chicory  with  coffee  is  very  general,  for  many 

343 


Raw  Coffee. 

Roasted  Coffee 

i-o8 

0-82 

9-55 

0-43 

8-46 

4-74 

mg 

6-90 

14-14 

I2'6o 

13-59 

9-87 

11-23 

0-87 

1-24 

37-95 

48-62 

3-74 

4-56 

8-98 

0-63 

lOO'OO 

100-00 

344  LABORATORY    WORK 

people  will  not  drink  coffee  without  chicory;  but  it  is  an  illegal 
and  fraudulent  adulteration  when  the  mixture  is  sold  as  coffee. 
Eighty  per  cent,  of  chicory  is  present  in  some  "  coffee  mixtures." 
The  .substance  is  employed  to  blacken  and  thicken  the  infusion, 
and  to  give  a  slightly  bitter  flavour;  but,  while  it  has  a  very 
similar  dietetic  value,  owing  to  the  absence  of  the  alkaloid,  it 
has  none  of  the  refreshing  and  stimulating  powers  of  coffee. 

There  are  se\-eral  well-marked  characteristics  of  chicory  which 
enable  its  presence  to  be  detected. 

1.  It  has  a  peculiar  and  distinct  odour,  different  to  that  of 
coffee. 

2.  The  characteristic  dotted  ducts  of  the  chicory  (Fig.  74) 
form  a  safe  and  rapid  means  of  detection  by  means  of  the  micro- 
scope, and  no  judgment  upon  the  presence  of  chicory  should 
ever  be  pronounced  without  this  evidence. 

3.  A  10  per  cent,  infusion  of  dried  chicory  (made  by  adding 
10  grammes  to  100  c.c.  of  water,  raising  to  the  boiling-point  and 
maintaining  at  that  temperature  for  thirty  seconds,  and  then 
filtering)  is  much  blacker  than  that  of  coffee,  and  its  specific 
gravity  at  15°  C  is  higher.  The  specific  gravity  of  such  a  chicory 
infusion  is  rarely  below  1018,  and  averages  about  1022,  while 
that  of  a  similar!}'  prepared  coffee  infusion  never  exceeds  loio, 
and  averages  about  1008-5.  The  specific  gravity  is  also  a  test 
for  the  presence  of  other  adulterants  which  have  rarely  been 
added  to  coffee — viz.,  ground  carrots,  beetroot,  parsnips,  turnips, 
and  mangel-wurzel,  the  infusions  of  which  ha\'e  a  specific  gravity 
of  1015  and  over.  It  is  obvious  that  chicory  must  be  in  con- 
siderable quantities  along  with  the  coffee  to  affect  the  specific 
gravity  of  the  whole  mixture  very  materially;  but  when  this  is 
the  case,  from  the  specific  gravity  the  extent  of  the  adulteration 
may  be  calculated.  Thus,  if  we  take  the  specific  gravity  of  the 
coffee  infusion  as  averaging  1008-5,  and  that  of  chicory  1022, 
a  sample  of  chicory'  has  a  specific  gravity  13-5  higher  than 
average  coffee.  How  much  chicory  is  probably  present  in  a 
mixture  with  a  specific  gravity  of  1012,  or  3-5  highei  than  average 
coffee  ? 

13*5=  100  per  cent,  of  chicory; 
.-.  3*5=  about  26  per  cent. 

4.  Roasted  chicory  sinks  in  water  at  once,  while  roasted  coffee 
floats  for  some  time,  owing  to  the  oil  in  the  coffee  preventing  the 


COFFEE  345 

particles  from  being  readily  wetted;  and  in  chicory  the  sediment 
in  the  cup  is  soft  and  pulpy,  while  that  of  coffee  is  hard  and 
gritty.  Moreover,  the  particles  of  chicory  as  they  sink  become 
almost  immediately  enveloped  in  a  light  brown  cloud,  which, 
forming  brown  streaks  in  the  water,  quickly  imparts  a  dark 
colour  to  it.  Coffee  will  take  a  much  longer  time  to  achieve  a 
similar  result — i.e.,  from  fifteen  to  twenty  minutes;  and  the 
other  sweet  roots  with  which  it  has  been  rarely  adulterated — 
i.e.,  mangel-wurzel,  carrots,  parsnips,  etc.- — will  require  the  lapse 
of  several  minutes.  Sometimes  a  little  oil  is  shaken  up  with  the 
ground  chicory,  which  prevents  it  sinking.  In  these  cases  the 
oil  can  be  extracted  by  ether,  and  the  material  then  tested  as 
to  the  readiness  and  extent  to  which  it  colours  water,  and  as 
to  the  character  of  the  sediment  formed. 

5.  A  useful  test  is  as  follows:  If  the  coffee  be  dried,  powdered 
and  passed  through  a  sieve  of  thirty  meshes  to  the  inch,  i  gramme 
infused  for  one  hour  in  20  c.c.  of  proof-spirit  will  give  an  infusion 
containing  19 "4  per  cent,  of  total  solids  if  the  sample  be  entirely 
coffee.  If  it  is  entirely  chicory,  the  total  solids  will  total  66-4  per 
cent. 

6.  The  substitutes  for  coffee  are  practically  devoid  of  caffein. 
This  may  be  determined  as  in  Tea. 

7.  Take  5  grammes  of  coffee,  and  pour  upon  it  about  25  c.c.  of 
boiling  water  and  filter,  then  to  the  filtrate  in  a  Nessler  glass  add 
acetate  of  lead  solution.  This  will  throw  down  the  colouring 
matter  of  the  coffee,  but  leave  that  of  the  chicory ;  and  the  latter 
can  be  estimated  by  comparing  the  colour  with  a  standard 
mixture  containing  known  quantities  of  chicory  (Albert  Smith). 

Roasted  beans,  acorns,  and  other  starches  have  rarely  been 
employed,  and  a  microscopic  examination,  together  with  the 
addition  of  iodine  to  the  infusion  (decolorized  by  boiling  with 
animal  charcoal),  would  readily  detect  them.  An  infusion  of 
pure  chicory  is  not  blued  by  iodine,  nor  is  a  strained  infusion  of 
coffee.  This  test  may  also  be  applied  as  follows:  Boil  the  coffee 
for  a  few  minutes  with  about  10  parts  of  water,  allow  the  infusion 
to  get  quite  cold,  add  dilute  sulphuric  acid,  and  then  drop  in 
some  strong  solution  of  the  permanganate  of  potassium  with 
agitation,  until  the  colouring  matter  is  nearly  destroyed,  when 
strain  and  add  iodine  (Allan). 

Burnt  sugar,  or  caramel,  has  been  added  to  improve  the 
colour,  aroma,  and  taste  of  the  infusion.     It  can  be  detected  by 


346 


LABORATORY  WORK 


the  fact  that  it  will  very  rapidly  and  deeply  colour  water.  A 
hand-lens  will  disclose  the  shining  particles  of  caramel  standing 
out  from  the  comparatively  dull  particles  of  the  ground  berry, 
and  if  the  former  are  picked  out  with  forceps  they  will  be  found 
quite  soluble  in  water. 

Artificial  coffee-beans  were  within  recent  years  placed  upon 
the  market;  they  were  made  from  a  paste  of  various  starches 


FIG.  73. — coffee:  cells  of  testa  and  cellular  structure. 

(X  ABOUT    200.) 

coloured  and  flavoured  with  a  little  coffee  and  chicory.  Warm 
water  caused  them  to  break  up.  Sometimes  berries  which  have 
been  exhausted  by  making  coffee  extract  are  sold. 

Sugar  syrup  has  been  employed  to  glaze  exhausted  beans,  and 
also  to  cause  the  unused  berries  to  retain  their  moisture. 


FIG.  74. — chicory:  dotted  ducts  and  cellular  structure. 
(x  about  200.) 

Coffee  extracts  are  deficient  in  caffein  and  extractives,  and 
may  be  adulterated  with  chicory,  caramel,  etc.;  salicylic  acid  is 
sometimes  added. 

Microscopical  Examination. — The  microscopical  characters  of 
the  raw  coffee  berry  are  distinctive.  The  testa  or  skin — portions 
of  which  are  always  ground  up  with  the  rest  of  the  berry — con- 
sists of  long  spindle  cells  with  tapering  rounded  extremities, 


COFFEE  347 

which  are  dovetailed  into  each  other.  Their  characters,  by  the 
J-inch  power,  are  shown  in  Fig.  73.  The  internal  cellular 
substance  of  the  berry  is  made  up  of  a  thick  areolar  tissue  the 
meshes  of  which  are  very  irregular  in  size  and  shape,  and  contain, 
in  addition  to  starch  granules,  yellow  angular  masses  and  an 
occasional  oil  globule ;  the  walls  of  this  mesh- work  are  somewhat 
beaded  in  appearance. 

In  chicory,  the  cellular  tissue,  the  large  dotted  ducts,  and  the 
lacteal  vessels  are  characteristic.  It  is  a  good  plan  to  soak  some 
of  the  mixture  of  coffee  and  chicory  in  sodium  hypochlorite 


FIG.  75. — LACTEAL  VESSELS  OF  CHICORY. 

solution  and  then  pick  out  the  pale  membranous  particles  and 
examine  these ;  or  the  mixture  may  be  thrown  on  to  water  in  a 
sediment  flask  and  the  particles  which  rapidly  sink  may  be 
specially  selected  for  examination. 

The  cellular  tissue  consists  of  an  oval  or  rounded  mesh-work, 
and  is  coarser  than  that  of  coffee.  The  dotted  ducts  appear  as 
jointed  tubes  marked  with  bars  and  possessing  extremities  which 
do  not  taper.  Similar  structures  are  found  in  roasted  beetroot. 
The  lacteal  tubes  are  long,  pale,  and  narrow  branching  tubes, 
which  are  filled  with  a  substance  called  "  latex." 


Cocoa. 

After  roasting,  the  husk  or  shell  of  the  cocoa-seeds  is  cracked  by 
machinery  and  then  separated  from  the  "  nibs." 

Cocoa-nibs,  on  analysis,  are  found  to  consist  mainly  of  the 
following  ingredients : 

Fat,  generally  amounting  to  about  50  per  cent. 

Albuminous  matter,  commonly  varying  from  12  to  16  per 
cent.     An   astringent  substance  resembling  tannin.     Cellulose, 


348  LABORATORY   WORK 

starch,  gum,  cocoa-reel  (a  substance  of  a  resinous  character, 
which  furnishes  the  colour  of  cocoa),  the  alkaloid  ("  theobro- 
mine," which  closely  resembles  the  alkaloids  of  tea  and  coffee, 
amounts  to  over  i  per  cent.,  and  varying  from  I'O  to  i'7  per  cent.), 
mineral  ash  (4  to  5  per  cent.),  and  water  (5  to  6  per  cent.). 

About  half  of  the  ash  is  soluble  in  cold  water. 

"  Prepared  cocoa  "  is  mixed  with  sugar  and  starch  (generally 
arrowroot  or  sago),  and  these  latter,  by  serving  to  disguise  the 
large  amount  of  fat,  which  disagrees  with  some  persons,  render 
it  more  generally  preferred.  Some  of  the  fat  can  be  readily 
removed  from  the  nib  by  heat  and  pressure,  and  this  plan  is  to 
be  advocated,  as  the  added  starch  does  not,  while  it  reduces  the 
percentage  of  fat,  provide  a  substance  of  equal  dietetic  value  to 
the  other  constituents  of  the  cocoa  which  it  displaces.  The 
microscope  will  at  once  detect  the  addition  of  such  foreign 
starches  (sago,  potato,  arrowroot)  by  disclosing  their  character- 

FIG.    76. COCOA    STARCH    CELLS.       ( X  ABOUT    200.) 

istic  granules.  Cocoa  is  sometimes  treated  with  alkali  ("  soluble 
cocoa  ")  with  the  object  of  emulsifying  the  fat  so  that  there  is 
less  tendency  for  it  to  separate  out  when  mixed  with  hot  water, 

An  admixture  with  starch  and  sugar  is  permissible  when  the 
sample  is  not  sold  as  pure  cocoa. 

The  ground  shells  of  the  cocoa-seeds  are  sometimes  added  as 
an  adulteration.  The  microscopic  examination  may  detect  this: 
and  certain  chemical  and  mechanical  tests  are  useful. 

The  amounts  of  fat,  total  ash  and  of  the  soluble  ash,  furnish 
useful  tests  of  its  purity.  In  the  case  of  the  ash  this  varies  con- 
siderably in  even  pure  samples,  but  it  is  usually  under  4  per  cent. 
The  soluble  ash  in  the  cold  water  extract  should  not  fall  below 
2  per  cent.  The  fat  in  "  prepared  cocoa  "  generally  amounts  to 
from  25  to  35  per  cent.,  but  as  little  as  15  per  cent,  has  been  found 
during  recent  years — a  circumstance  which  is  probably  due  to  the 
ready  sale  of  the  fat  extracted. 

The  theobromine  may  be  estimated  by  previously  removing 


COCOA  349 

the  fat  and  caffcin  by  petroleum  spirit  and  drying  the  extract 
over  the  water-bath;  the  residue  not  affected  by  the  petroleum 
is  then  extracted  with  chloroform  for  four  hours  in  a  Soxhlet; 
the  chloroform  is  evaporated  off,  the  residue  is  boiled  several 
times  with  water,  and  to  this  the  water  in  which  the  fatty  residue 
has  also  been  boiled  is  added ;  after  evaporating  to  dryness  in  a 
platinum  dish,  the  residue  is  weighed  as  theobromine  (Diesing). 

Chocolate  is  cocoa  from  which  much  of  the  fat  has  been  re- 
moved ;  the  paste  remaining  is  then  mixed  up  with  a  considerable 
quantity  of  sugar  and  flavouring  substances.  It  is  liable  to  be 
attacked  by  the  larvae  of  the  chocolate  moth,  Ephesiia  elutella. 
Inferior  chocolate  may  be  very  deficient  in  cocoa. 

Chocolate  may  be  adulterated  with  cocoa-shell,  foreign  starches, 
or  foreign  fats. 

Microscopically  the  small  starch  granules  of  cocoa  may  occa- 
sionally be  seen  massed  together  in  the  cellular  areolar  tissue, 
which,  under  a  high  power,  is  seen  to  be  hexagonal.  The 
appearance  of  the  granules  is  shown  in  Fig.  76. 

The  most  external  layer  of  the  husk  of  the  cocoa-bean  con- 
sists of  long,  flat,  quadrangular  cells;  but  the  bulk  is  made  up  of 
large,  distinct,  and  rounded  mucilage  cells. 


CHAPTER  XII 

tea— infants'  foods 
Tea.   ' 

The  leaves  of  the  tea-plant  {Thea  sinensis),  as  they  find  their 
way  into  our  markets,  are  generally  mixed  with  some  of  the 
flower-buds,  together  with  numerous  small  stems  of  the  plant. 
The  difference  between  black  and  green  teas  is  entirely  due  to 
the  method  of  preparation,  for  they  are  both  derived  from  the 
same  plant. 

An  average  sample  of  black  tea  shows  about  the  following 
percentages  of  the  two  most  important  and  characteristic  con- 
stituents : 

Tannin,  6  to  12  per  cent. 

Thein,  2  to  3  per  cent. 

Experiments  in  the  Lancet  laboratory  indicate  that  the  caffein 
is  largely  in  combination  with  the  tannin,  as  a  caffein-tannate. 

The  ash  is  about  6  per  cent.,  or  a  trifle  over;  and  the  moisture 
commonly  amounts  to  10  per  cent. 

In  the  case  of  green  tea,  the  thein  and  moisture  are  generally 
less  and  the  tannin  about  double  that  in  black  tea. 

Scott  Tebb  has  shown  by  experiments  reproducing  the  con- 
ditions under  which  tea  is  ordinarily  prepared  for  drinking,  that 
China  tea  generally  furnishes  a  little  less  alkaloid  and  often  nearly 
20  per  cent,  less  tannin;  but  that  the  analytical  results  obtained 
from  China  and  Indian  teas  may  approximate  closely. 

Thein  is  the  alkaloid  from  which  tea  obtains  its  most  valued 
properties;  the  substance  has  been  estimated  as  high  as  6  per 
cent,  in  some  samples.  The  caffein  of  coffee  and  the  thein  of  tea 
are  apparently  the  same  substance. 

The  other  constituents  of  the  tea  leaf  are :  Cellulose,  vegetable 
albumin,  extractives  (by  alcohol),  chlorophyll  and  resin,  pectin 
and  pectic^acid,  dextrin  or  gum  (Bell). 

350 


TEA 


151 


An  infusion  of  tea  leaves  may  be  made  by  boiling  2  grammes 
of  powdered  tea  in  lOO  c.c.  of  water  for  one  hour  in  a  flask 
attached  to  a  reflux  condenser,  filtering  while  hot  and  repeating 
until  no  more  colouring  matter  is  extracted. 

Such  an  infusion  of  the  leaves  will  be  found  to  contain  the 
dextrin  or  gum,  tannin,  thein,  most  of  the  salts  and  some  of  the 
albuminous  substances,  pectin,  etc. 

A  good  judge  of  tea  will  form  a  ready  and  approximately 
accurate  estimation  of  its  purity  and  genuineness  by  the  odour 
and  taste  of  a  fresh  infusion. 


FIG.    77. THE    ELDER    LEAF. 

(after    BELL.) 


FIG.    78. THE    WILLOW    LEAF. 

(after    BELL.) 


It  does  not  appear  to  be  an  easy  matter  for  adulteration  to 
be  practised  in  this  connection,  and  it  is  now  practically  non- 
existent ;  yet  formerly  there  were  probably  few  articles  of  com- 
merce less  systematically  exposed  to  fraudulent  practices. 

The  admixture  with  foreign  leaves,  and  the  addition  of  leaves 
which  had  been  already  infused,  were  forms  of  sophistication 
much  practised  in  the  past.  A  low  magnifying  power  suffices 
to  disclose  the  structural  characters  of  different  leaves,  and 
fortunately  the  tea  leaf  possesses  characteristics  which  serve  to 
distinguish  it  from  others;  the  differences  are  slight,  however, 
and  may  be  readily  overlooked,  especially  when  the  leaves  of 
the  elder,  willow  and  sloe — -which  are  those  that  have  been 
most  commonly  employed — are  selected  to  serve  the  purposes 
of  adulteration. 


352  LABORATORY   WORK 

The  common  method  of  examination  is  to  soak  the  leaves  in 
warni  water,  and  to  spread  them  out  between  glass  slides,  when, 
by  holding  them  up  to  the  light,  all  the  chief  characters,  including 
the  venation,  can  commonly  be  discerned  if  a  hand-lens  is  em- 
ployed ;  it  is  often  necessary,  however,  to  proceed  to  a  low  power 
of  the  microscope  before  a  definite  conclusion  can  be  arrived  at. 

It  assists  in  the  detection  of  the  characteristic  structure  of  the 
leaves  if  they  are  previously  soaked  in  a  warm  solution  of  sodium 
hypochlorite. 

The  characters  of  the  tea  leaf,  when  thus  examined,  are  these : 
The  shape  is  elliptical;  it  averages  from  about  i  to  2  inches  in 


FIG.  79. THE  SLOE  LEAF.  FIG.  8o. THE  TEA    LEAF. 

(after    BELL.)  (AFTER    BELL.) 

length  and  from  \  to  i  inch  in  breadth;  the  margin  of  the  leaf 
shows  distinct  serrations,  each  of  which  is  surmounted  by  a 
small  spine,  and  these  serrations  do  not  quite  extend  to  the  point 
of  attachment  of  the  stalk;  the  apex  is  slightly  emarginate;  the 
primary  veins  come  off  dichotomously  from  the  midrib,  and  then, 
branching  off,  form  a  markedly  looped  network  extending  to  near 
the  margin  of  the  leaf,  where,  by  bending  back,  they  leave  a 
narrow  clear  space. 

Under  the  microscope  the  leaf  shows  an  epidermic  layer  of 
flattened  cells  possessing  well-marked  sinuous  outlines;  coming 
off  from  a  few  of  these  cells  are  long  slender  unicellular  hairs. 
On  the  under  surface  of  the  leaf  there  are  many  oval  stomata 
visible  (Fig.  81). 


TEA  353 

The  presence  of  long-branched  cells,  called  idioblasls,  will 
also  serve  to  identify  tea  from  the  leaves  which  have  been  most 
commonly  used  to  adulterate  it.  A  section  through  the  thick- 
ness of  the  leaf  should  be  cut  near  the  midrib;  the  section  should 
be  soaked  in  strong  potassic-hydrate  solution  and  mounted  and 
examined  with  the  |-inch  power,  when  the  appearance  shown  in 
Fig.  82  will  be  observed  in  the  case  of  the  tea  leaf. 


FIG.    81. THE    EPIDERMIS    OF    THE    UNDER    SURFACE    OF    THE    TEA 

LEAF,    SHOWING    HAIRS    AND    STOMATA.       (X25O.) 

The  most  distinctive  characteristics  of  the  tea  leaf  are:  the 
spine-mounted  serrations,  which  terminate  a  little  before  the 
point  of  attachment  of  the  stalk;  the  looped  venation;  the 
notched  apex;  the  long  slender  unicellular  hairs;  and  the  large 
number  of  stomata  upon  its  under  surface. 

The  leaves  of  the  elder,  willow,  and  sloe  are  shown  in  Figs,  yy, 
78,  and  79,  in  order  that  they  may  be  compared  with  the  tea 


FIG.    82. SECTION    OF    A    TEA    LEAF,    SHOWING    IDIOBLASTS.        (X  I50.) 

leaf  and  with  each  other;  the  differences  will  be  seen  to  be 
shght. 

The  leaf  of  the  elder  is  seen  to  differ  in  the  following  respects : 
Its  shape  is  ovate ;  the  margin  is  sharply  dentated  and  the  apex 
is  pointed;  the  leaf  is,  moreover,  seen  to  be  asymmetrical,  due 
to  the  fact  that  one  lateral  half  of  it  is  attached  lower  dowTi  the 
midrib  than  the  other. 

23 


354  LABORATORY   WORK 

The  leaf  of  the  willoic  differs  in  the  following  respects:  It  is 
elliptico-lanccolate  in  shape,  with  a  pointed  apex,  and  its  contour 
presents  shallow  serrations. 

The  leaf  of  the  sloe  is  in  shape  similar  to  that  of  the  willow, 
and  the  margin  is  slightly  more  deeply  serrated  than  that  of  the 
tea  leaf. 

"  Lie-tea  "  is  the  name  given  to  a  mixture  of  tea-dust  with 
other  leaves,  claj',  sand,  etc.,  and  made  up  into  small  masses 
with  gum  and  starch. 

The  employment  of  used  leaves  is  a  more  difficult  matter  to 
detect,  as  they  may  be  prepared  to  resemble  those  which  are 
unused.  By  uniforml}-  colouring  or  "  facing  "  them — in  the 
case  of  green  teas,  by  indigo,  aniline  dyes,  a  mixture  of  Prussian 
blue,  turmeric,  and  sulphate  of  lime,  and  in  the  case  of  black  teas 
with  blacklead — their  appearance  has  been  made  to  closely 
resemble  that  of  unused  leaves;  but  this  "  facing  "  is  now  rarely, 
if  ever,  done.  Old  leaves  have  been  re-rolled  and  worked  up  with 
sand  and  gum ;  the  sand  or  quartz  serves  the  purpose  of  furnishing 
the  stiffness  of  the  natural  unexhausted  leaf  when  dried,  and  the 
gum,  while  also  aiding  in  this,  imparts  a  gloss  to  the  otherwise 
dull-looking  leaf. 

The  task  of  detecting  leaves  which  have  been  previously 
exhausted  and  not  subsequently  made  up  is  well-nigh  impossible 
to  achieve  when  these  are  only  added  in  reasonable  quantity;  for 
genuine  samples  of  tea  vary  so  much  as  to  the  relative  amounts  of 
their  constituents,  that  some  samples  may  have  been  partially 
exhausted  and  yet  yield  more  extract  to  boiling  water  than  other 
very  poor  but  genuine  samples. 

Most  will  probably  be  learnt  of  this  form  of  adulteration  by 
the  analysis  of  the  ash  of  the  leaves.  Bell  found  that  in  average 
samples  of  genuine  teas  (dried  at  ioo°  C.)  this  never  reached 
8  per  cent.,  and  was  generally  from  47  to  6-2  per  cent.;  and  the 
Society  of  Public  Analysts  has  advocated  8  per  cent,  as  the  limit. 
The  ash  soluble  in  water  does  not  fall  below  3  per  cent.,  by  weight, 
of  tea,  or  40  per  cent,  of  the  ash.  It  follows  of  necessity  that  a 
sample  of  tea  containing  much  exhausted  leaf  will  show  a  re- 
duction below  3  per  cent,  of  soluble  ash. 

The  ash  should  be  estimated  by  taking  10  grammes  of  tea, 
gently  incinerating  this  in  a  platinum  dish  and  weighing  the 
mineral  residue,  which  is  generally  grey  or  greenish  in  colour.  In 
"  faced  "  teas  the  ash  is  sometimes  10  per  cent.,  and  in  "  lie-tea  " 


TEA  355 

it  may  amount  to  30  per  cent.;  whereas  in  exhausted  tea  it  is 
rarely  above  o-8  per  cent.  The  ash  should  then  be  treated  with 
boiling  water  and  the  whole  filtered  through  a  small  Swedish 
filter-paper ;  the  insoluble  part  must  next  be  thoroughly  washed 
on  the  filter,  re-ignited  and  weighed ;  the  difference  between  the 
weight  obtained  and  that  of  the  total  ash  will  represent  soluble 
ash.  If  the  insoluble  residue  is  boiled  with  dilute  hydrochloric 
acid,  that  which  still  remains  insoluble  (consisting  mostly  of  sand 
and  quartz)  should  not  much  exceed  i  per  cent. 

The  estimation  of  thein  is  also  of  value  where  the  use  of  ex- 
hausted leaves  is  suspected .  Five  grammes  of  the  finely  powdered 
and  dried  tea  are  three  times  extracted  with  about  300  c.c.  of 
boiling  water  in  a  flask  fitted  to  a  reflux  condenser,  each  extrac- 
tion occupying  two  hours;  the  united  extracts  are  then  pre- 
cipitated with  neutral  lead  acetate,  and  the  liquid  again  boiled 
for  ten  minutes  and  filtered;  the  filtrate  is  freed  from  lead  by 
sulphuretted  hydrogen  and  evaporated  to  dryness  on  the  water- 
bath  with  freshly-ignited  magnesia  and  clean  coarse  sand;  the 
dry  residue  (finely  powdered)  is  then  thoroughly  extracted  with 
chloroform  in  Soxhlet's  apparatus.  The  residue,  after  evapora- 
ting the  chloroform  extract,  is  boiled  with  water,  filtered,  and  the 
filtrate  evaporated  down  and  dried  at  a  temperature  not  exceed- 
ing 100°  C.  and  weighed.  Under  the  microscope  the  thein 
appears  as  long,  white,  silky  needles. 

It  is  of  great  importance  that  the  preliminary  extraction  be 
made  with  the  greatest  thoroughness,  on  account  of  the  obstinacy 
with  which  a  little  of  the  alkaloid  is  apt  to  be  retained  by  the 
vegetable  tissue. 

Dvorkovitch,  when  estimating  thein  in  tea,  washes  the  extract 
with  petroleum  ether,  in  order  to  remove  the  oil  and  any  traces 
of  the  brown  substance  found  in  tea. 

A  simple  micro-chemical  method  for  the  detection  of  thein 
or  caffein,  which  is  rapid  and  requires  only  a  small  amount  of 
the  original  material,  is  to  place  a  tea  leaf  (or  a  similar  quantity 
of  the  substance  to  be  examined)  on  a  watch-glass  covered  with 
another  watch-glass  of  similar  size,  and  to  heat  for  five  minutes 
over  a  small  flame,  the  glasses  being  supported  on  a  wire  gauze 
about  7  centimetres  above  the  source  of  heat.  The  upper  cover- 
glass  will  then  be  found  to  show  numerous  droplets  of  con- 
densed liquid;  in  ten  minutes  fine  needle-shaped  crystals  \^dll 
appear,  and  after  fifteen  minutes  a  good  crop  of  these  will  be 


356  LABORATORY   WORK 

shown  on  microscopical  examination.  Exhausted  infused  tea 
leaves  show  no  sign  of  such  crystalline  sublimate.  Coffee  berries 
and  the  leaves  of  the  coffee-plant,  kola-nuts,  guarana  and  mate, 
all  give  a  characteristic  sublimate  of  caffein  when  treated  in  this 
manner.  By  applying  cold  water  to  the  outside  of  the  upper 
cover-glass,  the  appearance  of  the  crystals  may  be  materially 
hastened.  That  the  sublimate  consists  of  caffein  may  be  proved 
by  the  usual  chemical  tests.  When,  for  instance,  caffein  is 
treated  with  bromine  water  (avoiding  excess)  and  the  liquid 
evaporated  to  dryness  over  the  water-bath,  a  yellowish  residue 
is  left,  which  becomes  crimson-red  on  further  heating,  and  is 
turn^  purple  by  ammonia.  On  adding  caustic  soda,  a  com- 
plete and  instant  discoloration  occurs. 

Sodium  carbonate  and  borax  have  been  added  to  deepen  the 
colour  of  the  infusion. 

The  natural  perfume  of  tea  is  sometimes  added  to,  and  ap- 
parently harmlessl3'so,  by  packing  the  leaves  with  certain  aromatic 
flowers,  which  are  generally  removed  before  the  tea  is  placed  upon 
the  market.  Catechu  may  be  added  so  as  to  strengthen  the 
infusion.  The  presence  of  catechu  may  be  detected,  except 
when  it  is  in  very  small  amount,  by  precipitating  an  infusion  of 
tea  leaves  by  a  solution  of  neutral  lead  acetate,  then  filtering 
and  treating  the  filtrate  with  a  drop  or  two  of  a  dilute  solution 
of  ferric  chloride.  A  bright  green  colour  appears  in  the  presence 
of  catechu,  which  ultimately  settles  as  a  precipitate  of  a  more 
sombre  hue. 

The  tannin  may  be  roughly  estimated  from  the  infusion  of  a 
weighed  quantity  of  tea,  from  which  it  may  be  precipitated  by 
gelatine;  about  40  per  cent,  of  the  precipitate,  when  collected 
and  dried,  will  consist  of  tannin. 

In  the  Lancet  laboratory  it  is  found  that  good  and  consistent 
results  are  obtained  by  taking  20  c.c.  of  the  fresh  infusion, 
adding  slight  excess  of  bicarbonate  of  soda  and  running  in  Jl 
iodine  solution  until  some  petroleum  ether  (shaken  after  each 
addition  with  the  mixture)  showed  a  slight  excess  of  iodine 
present  by  the  well-known  violet  colour.  The  factor  for 
tannin  is  each  c.c.  of  -^  iodine  used  multiplied  by  0-0021. 

A  precise  estimation  of  tannin  is  difficult  and  unsatisfactory. 
Lowenthal's  process,  as  modified  by  Proctor,  is  one  of  the  best. 
In  this  method  it  is  ascertained  how  much  permanganate  of 
potassium  is  reduced  by  tannic  acid  and  other  readily  oxidizable 


INFANTS     FOODS  357 

substances  in  the  infusion;  the  available  tannin  is  then  pre- 
cipitated by  gelatine,  and  then  it  is  seen  how  much  permanganate 
is  used  up,  the  difference  representing  the  amount  of  perman- 
ganate decomposed  by  tannin. 

Infants'  Foods. 

There  are  many  proprietary  articles  upon  the  market  which 
have  a  large  sale  as  "  Infants'  Foods,"  and  they  vary  consider- 
ably in  their  value  as  nutrients.  Condensed  milk  has  perhaps 
the  largest  sale  {vide  p.  245) .  There  is  no  legal  limit  fixed  as  to  the 
amount  of  milk  constituents  which  such  preparations  should 
contain,  but  considering  the  dilutions  generally  recommended 
for  the  purposes  of  infant  feeding,  the  fat  ought  not  to  be  less 
than  10,  nor  the  non-fatty  milk  solids  less  than  25*5  per  cent. 

It  is  of  great  importance  that  little  starch  should  enter  into 
the  composition  of  infants'  foods,  for  the  reason  that  infants  are 
incapable  of  properly  digesting  it.  The  starch  is  therefore  partly 
or  wholly  transformed  into  dextrine  or  malt  sugar.  The  presence 
of  starch  may  be  best  ascertained  by  the  microscope,  especially 
if  a  drop  of  iodine  solution  is  allowed  to  run  under  the  cover-glass. 
The  nature  of  the  starch  employed  may  also  be  detected  by  the 
microscopic  examination.  A  quantitative  estimation  may  be 
made  by  separating  the  sugar  and  other  soluble  matter  from  the 
preparation  by  cold  water,  and  drying  the  residue  (containing 
starch)  by  prolonged  heating  in  a  water-bath;  an  aliquot  part 
(about  0-5  gramme)  of  this  is  then  inverted,  and  the  amount  of 
starch  calculated  by  multiplying  the  amount  of  invert  sugar 
(estimated  by  Fehling's  method,  vide  pp.  340,  341)  by  0-9. 

There  should  be  phosphates  in  these  preparations.  They  may 
be  dissolved  out  from  the  ash  by  nitric  acid,  and  estimated  by 
the  method  employed  in  water  analysis.  All  chemical  preserva- 
tives should  be  absent. 

The  total  nitrogen  may  be  estimated  by  Kjeldahl's  process. 

Most  of  the  "  Infant  Foods  "  at  present  on  the  market  con- 
sist of  either  desiccated  cow's  milk  with  sugar,  cream,  and  malted 
flour;  or  are  malted  farinaceous  foods;  or  are  little  more  than 
baked  flours.  The  proteid  material  generally  falls  between  8  to 
14  per  cent.;  the  fat  from  i  to  12  per  cent.;  the  carbo-hydrates 
from  70  to  82  per  cent.;  and  the  mineral  ash  from  i  to  3  per  cent. 


CHAPTER  XIII 

PRESERVED  AND  TINNED  PROVISIONS 

The  preservation  of  sterilized  food  in  tins  or  cans  is  a  valuable 
means  of  saving  a  large  amount  of  food,  and  it  thus  cheapens 
living.  Given  that  wholesome  food  is  always  used,  and  the 
process  of  canning  and  sterilization  is  efficiently  conducted,  the 
material  remains  good  for  a  long  period;  but  the  exclusive  use  of 
canned  meats  may  lead  to  scurvy. 

Articles  of  food,  when  thus  preserved,  may  be  unwholesome 
from  the  following  causes : 

1.  Changes  in  the  food  itself,  owing  to  the  development  of 
ptomaines  or  toxins — these  may  be  present  prior  to  canning, 
or  they  may  develop  subsequent  to  canning,  either  before  the  tin 
is  opened,  or  very  shortly  afterwards. 

2.  The  addition  of  harmful  chemical  antiseptics  to  preserve  the 
contents. 

3.  The  addition  of  harmful  substances  employed  as  colouring 
agents. 

4.  Impurities  yielded  by  "  tins,"  or  the  solder  used  in  their 
manufacture.  By  the  action  of  the  juices  upon  the  tins,  tin, 
lead,  or  even  arsenic,  may  be  taken  up  from  the  tins  and  solder. 
It  is  the  vegetable  acids  naturally  in  the  food,  those  that  are 
formed  during  fermentation  of  vegetable  matter,  or  agents  which 
are  added  for  preservative  purposes  (vinegar  and  oil)  which  act 
upon  the  metals ;  and  this  action  may  be  increased  by  the  galvan- 
ism which  is  sometimes  set  up  between  the  metals  present.  Tinned 
asparagus,  tomatoes,  pears,  cherries,  plums,  and  apricots  are 
especially  liable  to  take  up  metals. 

1  he  contents  of  the  tins  are  hermetically  sealed  down  by  solder 
at  a  high  temperature,  and  the  partial  vacuum  thus  created  in 
the  tins  is  evidenced  by  their  tops  and  bottoms  being  slightly 
depressed  from  the  outside;  should,  however,  there  be  any  flaw 

358 


PRESERVED    AND   TINNED    PROVISIONS  35') 

in  the  tins,  or  a  solder  seal  be  imperfectly  applied,  or  should  the 
heating  process  be  but  partially  performed,  tlicn  the  contents 
may  go  bad,  and  in  the  latter  case,  owing  to  the  accumulation 
of  the  gases  of  putrefaction,  the  tops  and  bottoms  of  the  tins 
become  quite  flat,  and  later  on  convex  outwards,  and  the  tin 
when  struck  may  give  out  a  hollow  or  drumlike  sound.  It  is  not 
difficult,  therefore,  in  some  cases  to  detect,  before  opening  them^ 
those  tins  in  which  the  contents  are  bad.  Bcveridge  accounts 
for  the  circumstance  that  tins  exposed  to  unduly  high  tempera- 
tures, subsequent  to  canning,  sometimes  become  "  blown,"  by 
the  fact  that  the  spores  of  Bacillus  cadaveris  sporogenes,  which  are 
very  resistant  to  heat,  may  not  develop  at  low  temperatures,  but 
rapidly  do  so  at  temperatures  of  about  37°  C.  He  therefore 
recommends  that  sample  tins  should  be  examined  after  incuba- 
tion at  37°  C.  for  a  fortnight. 

Minor  degrees  of  gas-formation  may  best  be  detected  by  per- 
forating the  tins  under  water,  when  small  bubbles  of  gas  will  be 
seen  to  rise.  Viry  maintains  that  putrefactive  changes  in  canned 
foods  may  take  place  without  the  formation  of  any  gas. 

The  bulging  of  tins,  though  generally  produced  by  the  forma- 
tion of  the  gases  of  putrefaction  ma}^  be  localized  and  due  to  rough 
treatment,  whereby  they  are  dented  and  the  contents  displaced. 
The  condition  may  also  be  due  to  the  freezing  of  tins  containing 
liquid  or  semi-liquid  food  (as  in  cold  storage) ;  the  tins  bulging 
from  the  expansion  of  the  frozen  liquid. 

It  seems  that  bulging  may  also,  in  exceptional  cases,  be  caused 
by  gas  produced  by  electrolytic  action  between  the  metal  of 
which  the  cans  are  composed  and  acids  in  the  contents.  (This 
has  occurred  in  condensed  milk.) 

As  blown  tins  have  been  punctured  to  allow  of  the  escape  of 
the  gases  produced  by  putrefaction,  and  then  re-sterilized  and 
resoldered,  it  has  been  said  that  cans  showing  two  solder  points 
are  suspicious;  but  in  the  event  of  such  a  fraudulent  practice  it 
is  generally  easier  to  melt  the  solder  over  the  original  blow-hole, 
and  then  resolder,  than  to  make  a  second  hole  and  solder  it,  and 
some  firms  invariably  make  a  second  blow-hole  (especially  in  flat 
tins).  An  accidental  splash  of  solder  may  simulate  a  second 
blow-hole. 

In  the  process  of  canning,  after  the  top  has  been  soldered  on 
and  the  small  hole  in  the  lid  closed  with  solder,  the  can  is  either 
placed  in  a  steam  retort  at  115°  C.  for  one  or  two  hours;  or  in  a 


360  LABORATORY    WORK 

boiling  solution  of  calcium  chloride  {105°  C.)  for  one  or  two  hours; 
or  in  ordinary-  boiling  water  for  four  hours.  The  contents  of  the 
tin  expand  and  the  sides  and  ends  slightly  bulge.  The  can  is  then 
taken  out  of  the  apparatus,  and  the  prick-hole  is  unsoldered  by 
the  application  of  a  hot  iron,  when  about  i  cubic  inch  of  heated 
air  escapes.  The  hole  is  soldered  up  afresh  and  the  can  put  back 
again  into  the  water-bath  or  steaming  apparatus  for  another  hour, 
and  the  sterilizing  and  cooking  process  completed.  For  blowing 
purposes  during  the  bathing  or  steaming  processes,  instead  of 
taking  the  trouble  to  expose  and  unsolder  the  prick-hole,  some 
firms  prefer  making  a  second  hole  either  at  the  side  or  at  the  other 
end  of  the  can. 

With  condensed  milk  and  with  jams  and  syrups  it  is  not 
absolutely  necessary  to  have  blow-holes,  and  in  some  brands 
none  are  to  be  found.  These  materials  are  already  cooked,  and 
are  poured  hot  into  the  cans,  which  have  concave  ends  when  the 
contents  arc  cooled  down.     The  sugar  acts  as  the  preservative. 

Nothing  short  of  opening  some  of  the  cans  will  enable  one  to 
express  a  safe  opinion  with  reference  to  the  contents.  From 
2  to  5  per  cent,  should  be  opened,  and  the  contents  in  some  cases 
examined  chemically  and  bacteriologically. 

When  the  tin  is  opened,  further  evidence  of  possible  danger 
in  the  consumption  of  the  contents  may  be  indicated  by  either 
an  offensive  odour,  a  loss  of  colour  or  darkening,  an  unnatural 
softness  of  the  contents,  or  a  blackening  or  corrosion  of  slaty- 
blue  discoloration  of  the  inside  of  the  tin  (which  should  be  silvery 
white).  The  darkening  is  often  due  to  sulphides  being  formed 
at  the  time  of  sterilization,  especially  when  the  meat  was  alkaline 
from  decomposition.  Any  gelatine  present  should  be  in  a  sohd 
condition. 

In  order  to  obtain  a  satisfactory  sample  of  the  contents,  the 
whole  of  them  should  be  twice  passed  through  a  fine  mincing 
machine,  and  then  ground  up  in  a  mortar.  The  reaction,  which 
in  the  case  of  meats  is  usually  acid,  may  be  expressed  in  terms 
of  lactic  acid  (i  c.c.  of  decinormal  soda  =  0-009  gramme  of  lactic 
acid),  The  mineral  ash  is  never  white  in  the  case  of  meat,  and 
its  reaction  should  be  alkaline.  In  estimating  the  fat,  2  grammes 
of  the  dried  material  are  extracted  in  Soxhlet's  apparatus.  The 
proteid  material  is  calculated  from  the  total  nitrogen  of  i  gramme 
obtained  by  Kjeldahl's  process. 


PRESERVED    AND    TINNED    PROVISIONS 


l6l 


The   Average  Percentage   Composition   of  Tinned   Meats 
(Beveridge). 


Water. 

Ash. 

Protein. 

Fat. 

Corned  beef     .  . 
Roast  beef 
Corned  mutton 
Roast  mutton 

Per  Cent. 
51-05 
58-23 
43-05 
46-22 

Per  Cent. 
3-56 
3-22 

2-39 
1-52 

Per  Cent. 

28-72 
26-75 
26-34 
26-50 

Per  Cent. 

1774 
12-90 
28-12 
25' 74 

It  is  very  important  that  the  tin  or  can  in  which  these  food- 
stuffs are  placed  should  be  satisfactory.  The  coating  of  tin 
should  be  properly  done,  so  that  no  flaws  are  perceptible  with  a 
magnifying-glass,  as  otherwise  the  iron  beneath  will  rust  through. 
Potassium  ferricyanide  solution  may  be  employed  to  demonstrate 
(by  its  bright  blue  precipitate  with  the  exposed  iron)  the  presence 
of  pin-hole  flaws.  The  tin  used  for  coating  ought  not  to  contain 
more  than  i  per  cent,  of  lead,  and  "  terne  plate  "  (two  of  tin  to 
one  of  lead)  should  be  prohibited.  The  solder  employed  ought 
not  to  contain  more  than  10  per  cent,  of  lead,  and  should  be 
confined  to  the  outside  of  the  can.  Cans  containing  very  acid 
juice — namely,  vinegar,  plum,  and  asparagus  juices — should  be 
lacquered  inside. 

The  soldering  should  be  performed  so  that  it  is  impossible 
for  it  to  reach  any  internal  surface  of  the  can;  and  in  the  majority 
of  tins  as  now  made,  this  is  only  possible  by  the  metal  or  soldering 
fluid  being  accessible  to  the  contents  of  the  can  in  the  operation 
of  closing  the  vent-hole.  Many  of  the  better  class  manufacturers 
provide  against  this  accident  by  means  of  a  solder-trap  con- 
sisting of  a  small,  cup-shaped  piece  of  tin  attached  immediately 
beneath  the  vent-hole. 

Poisonous  symptoms  have  been  traced  to  the  presence  of  tin 
in  preserved  foods.  Where  the  metal  is  eroded,  which  is  com- 
monly at  spots  where  it  has  been  in  contact  with  fat,  the  cause  of 
the  erosion  is  due  to  the  formation  of  basic  stannous  chloride. 
A  tin  sulphide  is  also  sometimes  formed  by  the  action  of  decom- 
posing albuminous  matters.  Varnished  tins  are  used  by  some 
French  manufacturers,  and  lead  has  sometimes  been  found  in  this 
varnish.  Tin  is  but  slightly  soluble  in  acetic  and  other  organic 
acids,  and  in  the  absence  of  oxygen;  and  its  absorption  is  very 
slight  in  the  gastro-intestinal  tract.     Instances  of  poisoning  have, 


362  LABORATORY   WORK 

however,  been  recorded  where  tin  to  the  amount  of  from  15  to  20 
grains  to  the  pound  was  found  in  the  food.  The  metal  has  little 
tendency  to  accumulate  in  the  system.  But  the  organic  acids  of 
preserved  fruit,  meat  extracts  and  essences  are  often  capable  of 
dissolving  many  grains  per  pound,  and  the  amount  taken  up 
increases  with  the  age  of  canning.  There  is  little  evidence  of 
danger  from  the  amounts  of  this  metal  which  are  generally  to  be 
found  in  canned  foods ;  but  it  must  be  borne  in  mind  that  obscure 
ailments,  possibly  associated  with  the  ingestion  of  such  foods,  are 
difficult  to  refer  to  their  specific  causes. 

The  erosion  of  the  tin  may  by  exposing  the  iron  enable  an 
electrolytic  action  to  lead  to  a  further  solution  of  tin. 

In  a  Report  of  the  Inspector  of  Foods  issued  by  the  Local 
Government  Board  in  1908,  the  special  attention  of  sanitary 
officers  and  public  analysts  is  directed  to  canned  food  of  more 
than  one  or  two  years  old;  and  it  is  stated  that  if  2  grains  of  tin 
per  pound  are  found,  it  may  be  taken  that  the  food  has  become 
potentially  deleterious  to  health.  In  the  estimation  of  tin  in 
such  material.  Dr.  Schryver  destroys  50  grammes  of  the  sample 
by  the  Kjeldahl  process;  he  then  dilutes  to  600  c.c,  treats  with 
sulphuretted  hydrogen,  and  allows  to  stand  overnight.  The  pre- 
cipitate of  tin  sulphide  is  collected,  washed,  and  dissolved  in  a 
small  quantity  of  hot  10  per  cent,  sodium  hydroxide  solution,  and 
the  sulphide  reprecipitated  with  glacial  acetic  acid  (this  removes 
silica,  etc.).  The  sulphide  is  then  collected  on  a  filter,  washed, 
dried,  oxidized,  and  the  tin  weighed  as  oxide. 

A  delicate  test  for  the  presence  of  tin  has  been  found  in  dinitro- 
diphenylaminesulphoxide.  Stannous  chloride  in  the  presence  of 
an  excess  of  hydrochloric  acid  furnishes  with  this  reagent  a 
brilliant  violet  colouring  matter. 

Tin-foil  has  been  shown  to  be  capable  of  furnishing  lead  to  sweets. 

The  unscientific  use  of  lead  in  the  composition  of  glaze  for 
enamelled  saucepans  and  dishes  used  in  cooking  and  in  the 
storing  of  food,  has  led  to  several  accidents.  The  fat  or  acidity 
of  food  may  dissolve  some  of  the  lead  in  the  glaze.  Glazed  vessels 
intended  for  domestic  purposes  should  not  yield  any  lead  when  a 
4  per  cent,  solution  of  acetic  acid  is  boiled  in  them  for  half  an 
hour.  This  test  is  by  no  means  too  stringent.  Glass  vessels  are 
the  most  hygienic  receptacles  in  which  food  may  be  stored ;  but 
their  use  entails  a  disadvantage  from  their  liability  to  break. 

It  is  not  necessary  to  repeat  here  the  means  of  testing  for  the 


PRESERVED    AND    TINNED    PROVISIONS  363 

various  metals,  since  their  characteristic  reactions  have  been 
seen  in  treating  of  Water.  The  presence  of  copper,  however,  can 
often  be  roughly  demonstrated  by  allowing  a  piece  of  steel,  such 
as  a  knife-blade,  to  lie  in  the  liquid  (acidified  with  sulphuric  acid) 
for  a  short  time,  and  noting  the  appearance  of  a  bronze  coloration 
upon  it.  To  estimate  the  amount,  extract  the  copper  from  the 
ash  of  a  considerable  amount  of  the  material;  the  grey  ash  should 
be  treated  with  concentrated  sulphuric  acid,  and  then  the  residual 
carbon  burnt  off  in  a  muffle.  The  ash  should  next  be  extracted 
with  nitro-hydrochloric  acid;  excess  of  ammonia  (1:3)  added; 
then  filter,  and  wash  with  dilute  ammonia.  Make  up  the  filtrate 
to  50  c.c,  and  transfer  to  a  Nessler  glass.  Then  match  the  blue 
tint  by  taking  a  second  Nessler  glass,  adding  ammonia  in  a  similar 
quantity  to  that  contained  in  the  other  Nessler  glass,  filling  up 
the  cylinder  to  the  50  c.c.  mark  with  distilled  water,  and  running 
in  the  necessary  amount  of  a  standard  copper  solution  (i  c.c.= 
o-i  milligramme  of  Cu). 

Aluminium  is  now  becoming  cheaper,  and  the  metal  is  ex- 
tremely well  adapted  for  making  into  "tins,"  pots,  canteens, 
etc.,  on  account  of  its  lightness,  ductility  and  malleability,  and 
owing  to  the  fact  that  its  bright  appearance  is  very  little  affected 
by  damp.  Alcohol  can  dissolve  up  the  metal  in  a  slight  degree, 
and  acids — even  acetic  and  lactic — have  a  similar  power,  though 
more  marked.  It  is  probable,  however,  that  even  in  the  latter 
case  there  is  not  sufficient  dissolved  to  give  rise  to  symptoms  of 
poisoning  under  the  common  conditions  of  food-potting,  for  the 
metal  is  not  a  very  poisonous  one.  It  also  appears  that  for 
ordinary  culinary  purposes  the  use  of  aluminium  cooking  vessels 
is  not  attended  by  any  risks  to  health. 

Doubtless  many  of  the  cases  of  poisoning  attributed  to  metals 
have  really  been  the  results  of  toxins,  etc.,  in  bad  food. 

Preserved  vegetables  have  commonly  been  found  to  be  coloiured 
(green)  by  copper  sulphate.  The  coloration  is  attributed  to  the 
formation  of  a  copper  salt  by  an  acid  derived  from  phyllocyanin 
(a  derivative  of  chlorophyll),  which  body  is  very  inert  and  in- 
soluble in  hydrochloric  acid.  Any  excess  of  copper  combines 
with  the  proteid  matter  to  form  copper  leguminate,  which  is 
practically  useless  for  colouring  piuposes. 

The  general  practice  is  as  follows:  The  peas  are  treated  with 
a  solution  of  cupric  sulphate ;  this  is  almost  immediately  poured 
off,   and   the    peas   are  subsequently  well  washed  with  water- 


364  LABORATORY   WORK 

They  are  next  boiled  in  their  tins,  and  then  soldered  up.  Some 
authorities  have  pronounced  in  favour  of  the  harmlessness  of  this 
emploj-ment  of  cupric  sulphate  when  the  amount  used  does  not 
exceed  2  grains  (about  §  grain  Cu)  to  the  pound  of  peas,  beans, 
spinach,  etc. ;  but  the  Departmental  Committee  appointed  in 
1S99  recommended  that  the  use  of  copper  for  colouring  food 
should  be  prohibited  (as  in  Germany  and  Austria).  In  small 
quantities  copper  is  found  naturally  in  certain  foods  (notably 
oysters),  and  Lehmann  assumes  that  nearly  A  grain  may  thus  be 
taken  in  dailj-. 

Sulphate  of  copper  acts  as  a  powerful  astringent  upon  the 
lining  membranes  of  the  stomach  and  intestines.  It  also  inter- 
feres with  digestion  by  reason  of  its  powers  of  inhibiting  the 
digestive  ferments,  even  when  present  in  very  small  quantity. 
In  large  doses,  or  in  smaller  doses  frequently  repeated,  it  is  an 
irritant  poison,  occasioning  sj-mptoms  closely  resembling  those 
due  to  lead-poisoning. 

W.  Ogilvie  and  ^M'Lean  Wilson  separated  the  copper  colouring 
matter  from  peas;  and  the  former,  by  experiments  upon  mice 
and  also  upon  his  own  bod3^  showed  that  the  organic  salts  of 
copper  thus  obtained  were  absorbed  by  the  alimentary  canal  of 
man  and  mice,  that  they  tend  to  accumulate  in  the  liver,  and  are 
mainly  excreted  in  the  urine  and  to  a  slight  extent  by  the  salivary 
glands.  The  copper  compound  is  soluble  in  artificial  gastric 
juice,  made  b}^  adding  Benger's  liquor  pepticus  to  0-2  per  cent. 
HCl  in  the  proportion  of  i  to  5,  the  whole  being  kept  at  a  tem- 
perature of  40°  C.  for  several  hours.  F.  A.  Cripps  has  shown 
that  90  per  cent,  of  the  copper  salts  are  thus  dissolved  in  two 
hours.  The  old  theory  that  the  copper  formed  with  the  Icgumen 
of  peas,  spinach,  etc.,  a  compound  which  is  quite  insoluble  by 
the  gastro-intestinal  secretions,  is  therefore  erroneous. 

It  is  by  no  means  uncommon  to  find  chemical  preservatives 
other  than  salt  and  saltpetre  in  meat  foods  packed  in  cans  or 
glass.  Of  these  preservatives  boron  compounds  constitute 
about  three-fourths  of  the  whole,  and  sulphite  preservatives 
constitute  almost  the  whole  of  the  remainder.  Their  presence 
points  to  the  probability  that  they  were  employed  to  overcome 
undesirable  conditions  either  in  the  meat  prior  to  canning  or 
occasioned  by  uncleanly  processes  or  insufficient  sterilization 
during  its  manufacture.  Sulphurous  acid  and  sulphites  are  some- 
times used  as  a  spray  or,  in  a  pickling  fluid,  either  to  keep  meat 
fresh  or  to  revivify  it  after  it  has  become  stale;  the  sulphiu^ous 


PRESERVED    AND    TINNED    PROVISIONS  365 

acid  employed  diminishes  in  amounts  on  keeping.  Hams  and 
bacon  are  sometimes  packed  between  thin  layers  of  powdered 
borax  when  they  arrive  in  this  country  from  abroad ;  and  Richards 
and  others  have  shown  that  boric  acid  which  has  been  in  contact 
with  hams  for  a  period  of  three  or  four  weeks  penetrates  their 
substance  to  a  very  considerable  degree,  reaching  even  the  most 
remote  parts  of  the  muscular  substance,  but  penetrating  only  to 
a  very  slight  extent  into  the  fat. 

Dr.  A.  W.  J.  MacFadden  states  in  a  report  to  the  Local  Govern- 
ment Board  (1908)  that  amounts  of  boric  acid  varying  from 
2-6  to  13-5  grains  per  pound  of  minced  and  mixed  ham  may 
result  from  mere  contact  with  the  preservative  in  the  packing- 
cases.  He  furthermore  expresses  the  view  that  certain  specified 
chemical  preservatives  should  not  be  used  in  the  preparation  of 
canned  meats,  and  that  in  any  schedule  of  prohibited  preservatives 
boron  compounds,  sulphites  and  preparations  of  sulphurous 
acids,  benzoic  acid  and  formalin  should  be  included. 

The  boric  acid  contained  in  these  foods  may  vary  from  a  frac- 
tion of  a  grain  per  pound  to  50  grains,  or  even  more,  the  amount 
depending  on  whether  the  preservative  has  been  employed  only 
as  a  packing  material  or  has,  in  addition,  been  used  in  the  curing 
of  the  meat. 

In  the  making  of  sausages  and  other  minced  meat  preparations 
there  is  a  temptation  to  obtain  raw  materials  cheaply  by  pur- 
chasing the  material  at  a  time  when  fresh  meats  have  reached 
the  limit  of  their  keeping  powers,  and  it  seems  a  fair  assumption 
that  where  this  material  is  sold  packed  in  cans  or  glass  and 
chemical  preservatives  are  found,  either  the  material  or  the 
canning  process  was  faulty,  as  in  the  alternative  case  their 
employment  is  quite  unnecessary. 

Dr.  A.  W.  J.  MacFadden,  in  reporting  upon  this  subject  to 
the  Local  Government  Board,  recommends  (1908)  that  if  boron 
preparations  are  used  for  the  preservation  of  sausages,  etc.,  a 
limit  of  I  per  cent,  of  boric  acid  (17-5  grains  per  pound)  would 
probably  be  ample  to  meet  the  different  trade  requirements,  and 
even  then  it  should  be  considered  as  to  whether  a  notification 
of  the  presence  of  the  preservatives  should  not  be  given  to  the 
purchaser. 

In  the  cheaper  brands  of  potted  meats  a  certain  quantitj^  of 
rice-flour  or  other  cereal,  varying  from  10  to  50  per  cent.,  or  even 
more,  is  generally  mixed  with  the  meat  which  they  contain. 


CHAPTER  XIV 

en e:\iical  antiseptics  and  colouring  agents  in  food 

The  employment  of  chemical  agents  which  will  prevent  the 
development  of  the  micro-organisms  concerned  in  putrefaction, 
and  termed  "  antiseptics,"  is  extensively  practised.  The  in- 
creasing use  of  these  substances  for  the  preservation  of  articles 
of  food,  and  the  necessity  of  keeping  a  rigid  control  over  this 
practice  in  the  interest  of  public  health,  has  rendered  the  detec- 
tion and  estimation  of  such  substances  a  very  important  matter. 
The  antiseptics  most  commonly  employed  are :  Borax  and  boric 
acid,  salicylates,  benzoates,  formaldehyde  (a  38  to  40  per  cent, 
solution  of  which  in  water  containing  a  small  quantity  of  methyl- 
alcohol  is  known  to  the  trade  as  "  formahn  "),  sulphurous  acid, 
bisulphite  of  calcium,  sodium  chloride,  and  vinegar;  but  salt- 
petre, sodium  fluoride  and  silico -fluorides,  spirits  of  wine,  and 
sulphate  of  copper,  have  all  been  employed.  Salicylic  acid  is 
depressing,  it  is  liable  to  be  cumulative  in  action,  and  it  has  an 
irritant  effect  upon  the  kidneys;  benzoic  acid  is  irritating;  sul- 
phurous acid  is  a  gastric  irritant ;  and  formaldehyde  has  a  strong 
tendency  to  combine  with  proteids  and  to  harden  them  and 
reduce  their  digestibihty.  Being  antiseptics,  and  therefore 
inimical  to  the  life  of  the  organisms  that  cause  putrefaction, 
they  must  exercise  a  retarding  effect  upon  the  activity  of  the 
enzymes  concerned  in  ordinary  digestion.*  Halliburton  has 
shown  that  as  little  as  0-05  per  cent,  of  formaldehyde  delays 
gastric  digestion;  and  outbreaks  of  dermatitis  have  been  attri- 
buted to  formalin  in  milk. 

It  is  certain  that  boric  acid,  salicylic  acid,  formic  aldehyde, 
etc.,  are  foreign  to  the  animal  body,  and  their  presence  must 

*  These  enzymes  or  digestive  ferments  are  non-living,  unorganized 
nitrogenous  bodies,  which  can  transform  other  organic  bodies  without 
exhausting  themselves. 

366 


CHEMICAL   ANTISEPTICS    IN    FOOD  367 

necessitate  a  departure  from  the  normal  chemistry  of  life.  They, 
moreover,  facilitate  an  uncleanly,  slovenly  treatment  of  food, 
and  render  it  possible  to  preserve  articles  in  incipient  decompo- 
sition for  some  time  with  every  appearance  of  freshness. 

There  is  almost  a  consensus  of  opinion  in  the  medical  pro- 
fession that  these  agents,  as  often  employed,  may  be  injurious  to 
health.  Boric  acid  and  its  salts  are  probably  the  least  harmful, 
and  doubtless  the  average  adult  could  take  a  few  grains  daily 
of  boric  acid  with  little,  if  any,  ill  consequences ;  but  these  anti- 
septics are  frequently  added  to  food-stuffs  by  ignorant  persons 
in  amounts  far  exceeding  those  necessary  to  effect  the  object 
desired.  Thus,  nearly  20  grains  of  boric  acid  have  been  found 
in  a  pint  of  milk,  doubtless  from  the  fact  that  the  milk  had  been 
dosed  by  the  farmer  in  the  first  place,  and  subsequently  by 
dairymen ;  52  grains  per  pound  have  been  found  in  potted  meat, 
and  150  grains  per  pound  in  cooked  tripe  imported  from  America. 
The  British  Pharmacopoeia  includes  boric  acid  and  borax  amongst 
its  drugs,  and  gives  the  dose  of  the  former  as  from  5  to  15  grains, 
and  of  the  latter  from  5  to  20  grains,  for  an  adult.  It  is  there- 
fore regarded  as  a  drug  capable  of  producing  physiological  effects 
upon  human  adults,  even  in  a  dose  of  5  grains. 

Boric  acid  is  to  some  extent  cumulative  for  a  few  days,  after 
which  the  daily  amount  eliminated  balances  the  amount  con- 
sumed. Eighty  per  cent,  of  the  boric  acid  and  borax  ingested 
is  eliminated  by  the  kidneys;  and  it  must  certainly  be  very 
harmful  to  those  suffering  from  kidney  disease.  It  may  be  men- 
tioned, further,  that  a  special  harmfulness  to  infants  is  indicated 
by  the  fact  that  borax  retards  to  some  extent  the  coagulation 
of  milk  by  the  rennet  ferment  of  the  gastric  juice,  and  that  as 
little  as  one  part  per  1,000  completely  inhibits  the  activity  of 
this  ferment  (Halliburton).  The  same  authority  has  shown  that 
when  boric  acid  is  added  to  milk  it  precipitates  the  lime  salts 
(which  are  required  by  infants  for  the  proper  formation  of  bone 
and  teeth)  as  the  insoluble  borate  of  calcium. 

Individual  susceptibility  to  the  drug  varies  considerably;  but 
there  is  a  considerable  amount  of  evidence,  of  an  experimental 
nature  upon  human  beings,  that  boric  acid  administered  in  doses 
of  15  grains  and  upwards  for  several  days  may  cause  headache, 
loss  of  appetite,  vomiting,  diarrhoea,  depression,  and  certain 
skin  eruptions.  The  writer  has  on  two  separate  occasions 
seriously  disturbed  his  digestion  by  taking  20  grains  of  boric 


368  LABORATORY   WORK 

acid  daily,  with  food,  for  only  three  days.  Doubtless  injury  to 
health  would  follow  upon  the  use  of  even  a  few  grains  daily 
when  administered  to  babies  in  milk.  Experiments  upon  human 
beings  have  produced  conflicting  results,  but  the  positive  evi- 
dence of  harm  obtained  b^-  many  far  outweighs  in  importance 
the  negative  results  which  have  been  obtained  by  others.  The 
latter  experiments  have  almost  all  of  them  been  upon  non- 
susceptible  adults  and  for  brief  periods;  and  there  is  no  evidence 
whatever  which  points  to  the  harmlessncss  of  these  drugs  upon 
infants  under  one  year  of  age  when  the  milk  (which  is  almost 
the  sole  article  of  their  diet)  is  dosed  with  boric  acid  for  long 
periods,  or  upon  adults  with  weak  stomachs  or  kidneys  who  take 
10  to  15  grains  several  times  a  week  in  food. 

Dr.  Wiley's  experiments  (1905),  carried  out  at  the  instance  of 
the  United  States  Department  of  Agriculture,  were  feeding 
experiments,  extending  over  twenty-eight  weeks,  upon  twelve 
healthy  young  men.  They  demonstrated  that  when  only  8  grains 
of  boric  acid  (or  its  equivalent  in  borax)  is  daily  taken  with  food 
for  seven  weeks  or  over,  in  some  instances  impairment  of  appe- 
tite with  gastro-intestinal  disturbance  and  headache  resulted, 
and  that  these  sensations  disappeared  when  the  preservative 
was  withdrawn. 

Dr.  Wiley  similarly  experimented  upon  the  effect  of  salicylic 
acid  and  the  salicylates.  For  thirty  days  salicylic  acid  was  given 
in  doses  gradually  increasing  from  3  to  30  grains.  A  loss  of 
weight  w^as  observed  in  almost  all  cases.  A  large  part  of  the 
salicylic  acid  was  excreted  unchanged  by  the  urine,  and  in  four 
men  a  tendency  was  shown  to  albuminuria.  He  found  that, 
when  added  to  food  even  in  small  quantities,  a  depressing  and 
harmful  effect  upon  health  and  digestion  and  a  disturbance  of 
the  general  metabolic  activities  of  the  body  were  manifested. 

In  1907  experiments  were  also  conducted  to  study  the  effects 
of  the  administration  of  sidphurous  acid  and  sulphites  with  food. 
The  preservative  was  administered  in  two  forms,  sodium  sulphite 
being  administered  in  capsules  to  one-half  the  men,  while  sul- 
phurous acid  was  added  to  the  drinking-water  of  the  others. 
The  average  daily  consumption  for  twenty  days  was  0-392  to 
0-628  gramme  of  sodium  sulphite,  and  0-213  to  0-343  gramme  of 
sulphur  dioxide.  The  medical  and  clinical  data,  in  Dr.  Wiley's 
opinion,  showed  that  sulphurous  acid  and  its  salts  in  the  free 
state  produce  harmful  effects,  the  metabolic  functions  being 


CHEMICAL  ANTISEPTICS   IN    FOOD  369 

disturbed  and  the  health  (particularly  the  digestion)  injuriously 
affected.  In  the  great  majority  of  cases  headache,  sensations 
of  dizziness  and  occasional  nausea,  indigestion,  pains  in  the 
stomach,  exhaustion  and  weakness  ensued.  In  some  cases  pal- 
pitation of  the  heart  and  other  unfavourable  symptoms  were 
noticed.  It  was  also  observed  that  there  was  a  marked  tendency 
to  albuminuria  and  a  reduction  in  the  quantity  of  hemoglobin 
and  in  the  number  of  red  and  white  blood-corpuscles  (particularly 
of  the  latter). 

Still  more  recently  the  same  observer  has  undertaken  an  in- 
vestigation into  the  effect  of  formic  aldehyde  upon  digestion  and 
the  health.  A  daily  dose  of  formaldehyde,  varying  from  100  to 
200  milligrammes,  was  given  in  milk  to  twelve  healthy  men. 
No  marked  symptoms  were  noticed  during  the  first  ten  days, 
but  then  headache  and  pain  in  the  stomach  and  intestines 
became  general,  in  many  cases  producing  cramps,  and  in  a  few 
cases  nausea  and  vomiting.  A  burning  sensation  in  the  throat 
was  reported  in  the  majority  of  cases,  and  in  four  of  the  subjects 
a  well-marked  itching  rash  appeared.  From  a  general  study  of 
all  the  data  Dr.  Wiley  draws  the  conclusion  that  the  admixture 
of  formaldehyde  with  food  is  injurious  to  health,  even  in  the  case 
of  healthy  young  men,  and  that  therefore  in  the  case  of  infants 
and  children  the  deleterious  effects  would  be  more  pro- 
nounced. The  metabohc  functions  were  disturbed  in  a  notable 
way. 

The  use  of  chemical  antiseptics  in  food  is  not  necessary.  Even 
dairy  produce  is  brought  from  Denmark,  etc.,  without  such  addi- 
tion, and  no  difaculty  is  experienced  by  milk  vendors  in  this 
country  and  abroad  in  selhng  to  the  consumer,  even  in  the  summer 
months,  milk  in  a  perfectly  fresh  state,  to  which  no  chemicals 
have  been  added. 

The  presence  of  chemical  preservatives  in  canned  articles  which 
have  been  sterilized  by  heat  indicate  that  the  addition  was  made, 
prior  to  canning,  to  check  decomposition.  With  good  material 
then-  use  is  entirely  unnecessary,  and  their  presence  is  not  ex- 
pected by  the  purchaser. 

But  it  is  not  only  in  one  article  of  a  meal  that  one  may  find 
chemical  preservatives.  At  breakfast  they  may  be  consumed  in 
milk,  butter,  ham,  or  bacon,  and  jam.  Thus,  though  the  quan- 
tity of  boric  acid  in  any  one  article  might  not  be  sufficient  to 
affect  health,  the  aggregate  amount  of  the  drug  taken  in  the 

24 


370  LABORATORY   WORK 

various  articles  of  the  meal  may  suffice ;  and  impaired  digestion 
and  nutrition  or  more  serious  disturbance  may  result. 

There  is  but  little  direct  evidence  in  the  community  of  boric 
acid  poisoning  from  food  because  the  symptoms  are  not  charac- 
teristic, and  may  be  due  to  many  causes,  and  in  any  particular 
case  their  origin  in  chemicid  preservatives  is  not  even  sus- 
pected. It  may  be  maintained  that  such  evidence  would  not  be 
lacking  if  the  employment  of  these  preservatives  in  food  had  in 
every  case  to  be  declared  to  the  public. 

Those  who  advocate  the  use  of  chemical  antiseptics  maintain 
that:  (i)  They  obviate  waste,  inasmuch  as  without  their  use  a 
large  amount  of  food  would  go  bad  and  have  to  be  destroyed. 
Milk,  it  is  said,  if  delivered  in  a  fresh  state,  will  not  keep  in  the 
homes  of  the  poor  without  antiseptics.  (2)  If  not  used,  the 
injury  resulting  from  the  consumption  of  fermenting  and  de- 
composing food  would  exceed  that  from  the  ingestion  of 
chemical  antiseptics.  (3)  The  experiments  hitherto  made  (more 
especially  upon  the  lower  animals)  furnish  quite  as  much 
evidence  of  the  harmlessness  of  these  agents  as  of  their  harm- 
fulness. 

None  of  these  arguments  are  of  much  weight.  Arguments  i 
and  2  are  belied  by  the  practical  experience  of  many  countries 
where  chemical  preservatives,  even  in  milk  and  butter,  are  dis- 
allowed. There  is  no  evidence  in  support  of  the  argument  that 
material  sold  as  fresh,  such  as  milk  and  fresh  sausages,  go  bad 
in  the  homes  of  the  poor.  The  poor  quickly  consume  what  they 
purchase;  they  do  not  buy  to  store.  As  to  Argument  3,  it  is 
impossible  to  argue  from  the  effects  which  feeding  experiments 
may  have  upon  the  lower  animals  to  those  which  may  be  pro- 
duced upon  very  young  or  sick  human  beings. 

Certainly,  if  the  use  of  these  chemical  preservatives  is  to  be 
sanctioned,  the  amounts  should  be  limited  by  law;  and  the  indi- 
vidual who  is  not  desirous  of  continuously  dosing  himself  with 
drugs  should  have  a  means  of  escape  from  them.  Their  presence, 
nature,  and  amount  should  be  legibly  set  out  upon  a  label,  and 
their  use  ought  most  certainly  to  be  prohibited  in  infants'  and 
invalids'  foods.  It  may  be  said,  however,  that  even  the  safe- 
guard of  a  label  assumes  an  amount  of  knowledge  and  discrimi- 
nation on  the  part  of  the  purchaser  which  is  unreasonable.  In 
New  South  Wales  (Public  Health  Act,  1902)  the  amounts  per- 
mitted are  as  follows:  Sulphurous  acid,  i|  grains;  salicylic  and 


CHEMICAL   ANTISEPTICS    IN    FOOD  37 1 

benzoic  acid,  i  grain;  and  boric  acid,  10  grains — per  pint  of  liquid 
or  per  pound  of  solid  food. 

The  Departmental  Committee  appowted  in  1899  to  consider  the 
subject  of  the  use  of  antiseptics  and  colouring  agents  in  fofjd, 
in  their  Report  (1901)  made  the  following  recommendations: 

1.  That  the  use  of  formaldehyde  or  formalin,  or  preparations 
thereof  in  food  or  drinks,  be  absolutely  prohibited. 

2.  That  salicylic  acid  be  not  used  in  a  greater  proportion  than 
I  grain  per  pint  in  liquid  food,  and  i  grain  per  pound  in  solid 
food;  its  presence  in  all  cases  to  be  declared. 

3.  That  the  use  of  any  preservative  or  colouring  matter  what- 
ever in  milk  offered  for  sale  in  the  United  Kingdon  be  con- 
stituted an  offence  under  the  Sale  of  Food  and  Drugs  Act. 

4.  That  the  only  preservative  which  it  shall  be  lawful  to  use 
in  cream  be  boric  acid,  or  mixtures  of  boric  acid  and  borax,  and 
in  amount  not  exceeding  0-25  per  cent.  (17-5  grains  to  the  pound), 
expressed  as  boric  acid;  the  amount  of  such  preservative  to  be 
notified  by  a  label  upon  the  vessel. 

5.  That  the  only  preservative  which  it  shall  be  lawful  to  use 
in  butter  and  margarine  be  boric  acid,  or  mixtures  of  boric  acid 
and  borax,  to  be  used  in  proportions  not  exceeding  0-5  per  cent. 
(35  grains  to  the  pound),  expressed  as  boric  acid. 

6.  That  in  the  case  of  all  dietetic  preparations  intended  for 
the  use  of  invalids  or  infants,  chemical  preservatives  of  all  kinds 
be  prohibited. 

7.  That  the  use  of  copper  salts  in  the  so-called  "  greening  "  of 
preserved  foods  be  prohibited. 

In  a  circular  issued  by  the  Local  Government  Board  in  1906  it 
is  stated  that  as  regards  formalin  and  boron  preservatives  the 
Board  are  advised  that  the  presence  in  milk  of  formalin  to  an 
amount  which  is  ascertained  by  examination  within  three  days 
of  collecting  the  sample  to  exceed  i  part  in  40,000  (i  part  in  100,000 
of  formic  aldehyde)  raises  a  strong  presumption  that  the  article 
has  been  rendered  injurious  to  health,  and  that  the  purchaser 
has  been  prejudiced,  in  the  above  sense;  and  that  a  similar 
presumption  is  raised  where  boron  preservatives  are  present  in 
milk  to  an  amount  exceeding  57  parts  of  boric  acid  per  100,000, 
(40  grains  per  gallon,  or  4  grains  to  the  pound) . 

Experiments  to  test  the  effect  of  chemical  antiseptics  on  health 
or  digestion  proceed  on  the  following  lines : 

I.  Solutions   of   starch   are   subjected   to   the   action   of   the 


372  LABORATORY    WORK 

salivary  and  pancreatic  ferments  at  appropriate  temperatures, 
and  a  comparison  is  made  of  the  amount  of  sugar  formed  before 
.  and  after  tlie  addition  of  the  preservatives.  Similar  experiments 
are  also  made  on  the  peptic  digestion  of  meat  and  the  pancreatic 
digestion  of  casein.  The  length  of  time  taken  in  the  conversion 
before  and  after  the  addition  of  the  antiseptic  should  also  be 
compared. 

2.  The  feeding  of  animals  on  food  to  which  known  quantities 
of  the  antiseptics  have  been  added,  and  then  either  (a)  weighing 
and  examining  the  faeces  in  order  to  ascertain  the  amount  of 
unassimilatcd  nitrogenous  and  fatty  matter;  {b)  noting  the  effect 
upon  the  body-weight  of  the  animals  from  day  to  day;  (c)  observ- 
ing the  effect  upon  the  intestinal  tract  (diarrhoea,  sickness)  or 
the  general  system  (loss  of  appetite,  discomfort,  etc.). 

3.  Experimenters  are  sometimes  prepared  to  experiment  upon 
themselves,  and  then  b}-  making  estimations  of  the  nitrogen  and 
fat  in  the  food  and  excreta  ascertain  whether  the  albuminous 
matter  and  fat  of  the  faeces  increase  in  amount. 

A  means  of  food  preservation  which  is  open  to  no  objections 
on  the  ground  of  public  health  is  cold  storage. 

The  heat  and  smoke  produced  by  burning  certain  woods  are 
used  for  preserving  fish  (herrings,  haddocks,  etc.),  and  the 
practice  is  proved  by  experience  to  be  unobjectionable.  The 
preservative  effects  of  smoke  appear  to  be  dependent  on  traces 
of  formic  aldehyde,  creosote,  etc.,  in  the  smoke. 

Salting  is  a  very  universal  method  of  preserving  meat,  fish, 
eggs,  olives,  etc. ;  vinegar  and  sugar  are  also  frequently  used,  and 
are  equally  unobjectionable.  As  decoloration  results  from  salting 
meat,  a  little  potassium  nitrate  (saltpetre)  is  commonly  added  to 
counteract  this;  and  in  small  quantities  it  is  unobjectionable. 

Many  methods  depend  upon  the  exclusion  of  air.  Coatings  of 
gelatine  or  glycerine,  of  collodion,  and  of  paraffin  wax  have  been 
employed  with  meat;  salts  which  chemically  combine  with 
oxygen  of  the  air,  such  as  sulphite  of  lime,  have  been  used;  and 
oils,  as  in  sardines,  to  exclude  air. 

The  chemical  preservatives  to  be  specially  sought  for  are:  In 
meats  (hams,  bacon,  sausage,  oysters,  shrimps,  etc.) — boric  acid 
and  borax,  sulphites,  and  sahcylic  acid.  Boric  acid  and  borax 
are  preferred  because  the}'  help  to  preser\'e  the  natural  colour 
better  than  common  salt,  etc.  In  milk  and  milk  products — 
boric  acid  and  borax,  formic  aldehyde,   and  occasionally  ben- 


CHEMICAL   ANTISEPTICS    IN    FOOD  373 

zoatcs ;  often  a  mixture  of  boric  acid  and  borax  is  employed  (sucii 
a  mixture  is  sold  as."  Glacialin  ").  In  jams,  jellies,  mincemeat, 
and  table  delicacies — salicylic  acid  and  benzoic  acid  or  their  salts, 
and  occasionally  boric  acid.  In  cider,  British  wines  and  fruit 
juices — salicylic  acid  and  sulphites.  In  fermented  beverages — 
salicylic  acid,  sulphites,  fluorides,  silico-fluorides,  and  boro- 
fluorides.  Saccharin  may  be  present  in  beers,  wines,  and 
sweetened  articles. 

Salicylic  acid  is  sparingly  soluble  in  water  and  unpleasant  to 
the  taste;  it  is  therefore  mostly  employed  in  highly  flavoured 
articles,  such  as  wines  and  jams. 

If  meat  is  packed  in  borax,  the  substance  of  the  lean  flesh  is 
penetrated  for  some  distance  by  the  antiseptic;  but  there  is  httle 
penetration  into  the  fat. 

Traces  (less  than  a  grain  to  the  pound)  of  boron  are  to  be 
found  in  nearly  all  fruits  and  vegetables. 

Boric  Acid  and  Borates. — Evaporate  100  c.c.  of  the  milk,  cider, 
wine,  etc.,  to  dryness,  after  rendering  alkaline  with  caustic  soda 
solution;  incinerate;  extract  the  ash  with  a  little  hydrochloric 
acid,  filter,  and  evaporate  the  filtrate  to  dryness.  Apply  a  very 
small  quantity  of  diluted  HCl  to  damp  the  ash;  add  a  few  drops 
of  a  fresh  saturated  turmeric  solution,  and  evaporate  to  dryness. 
The  dried  residue  is  brownish-red;  and  a  transient  blue  colour 
results,  changing  to  a  green,  when  a  little  water  and  alkali  are 
added  to  the  residue.  Or,  after  adding  just  sufficient  hydro- 
chloric acid  to  the  aqueous  extract  of  the  ash  to  furnish  slight 
acidity,  dip  in  a  piece  of  turmeric  paper,  dry  this  at  a  gentle 
heat,  when  it  turns  a  reddish  colour,  changing  to  a  dark  bluish- 
green  on  moistening  with  an  alkali. 

C.  E.  Cassal  and  H.  Gerrans  find  that  an  intense  magenta-red 
colour  is  produced  on  treating  solutions  containing  boric  acid 
with  curcumin  (or  ordinary  turmeric)  and  oxalic  acid,  and  dr3dng 
the  mixture  on  the  water-bath.  The  colour  is  different  to  that 
obtained  by  the  application  of  the  ordinary  turmeric  test  for 
boric  acid,  and  the  reaction  is  far  more  delicate,  extremely 
minute  quantities  of  boric  acid  being  easily  detected.  In  apply- 
ing the  test  for  the  detection  of  free  or  combined  boric  acid  in 
milk  and  other  food  products,  it  is  convenient  as  a  rule  to  operate 
on  an  ash.  The  ash  is  treated  with  a  few  drops  of  (i)  dilute 
hydrochloric  acid,  (2)  saturated  solution  of  oxalic  acid,  and 
(3)  alcoholic  solution  of  curcumin  or  turmeric;  and  the  mixture 


374  LABORATORY   WORK 

is  dried  on  tlie  watcr-batli  and  taken  up  with  a  little  alcohol.  In 
cases  where  the  amount  of  boric  acid  is  very  small,  the  substance 
(the  ash  of  which  is  to  be  operated  upon)  sliould  be  made  alkaline 
with  a  solution  of  barium  hydroxide  prior  to  evaporation  and 
incineration. 

All  distillation,  evaporation,  or  incineration  methods  result  in 
some  loss  of  boric  acid  and  therefore  underestimate  results. 
A.  W.  Stokes  recommends  the  following  method;  Place  lo  to 
20  grammes  of  milk  or  cream  in  a  tube,  add  four  times  the  bulk 
of  hot  methvlated  spirit  and  0-5  c.c.  of  normal  sulphuric  acid. 
This  latter  is  used  to  turn  out  the  boric  acid  from  any  of  its 
compounds — borax,  for  instance.  Shake  vigorously,  rotate  in  a 
centrifugal  apparatus,  or  let  settle  for  an  hour.  Filter  through 
a  dry  filter-paper,  pouring  off  the  liquid  only.  To  the  residue  in 
the  tube  add  a  little  hot  methylated  spirit,  shake,  pour  on  to  the 
filter,  and  wash  with  a  little  hot  methylated  spirit.  The  filtrate 
will,  if  kept  hot,  be  quite  clear,  and  it  will  now  contain  all  the 
boric  acid.  Add  0-5  c.c.  of  strong  phenolphthalein  solution  to 
the  hot  filtrate,  and  carefully  titrate  (while  hot)  with  decinormal 
soda  solution  till  there  is  a  slight  permanent  pink  colour.  With 
a  little  care  and  experience  it  is  quite  possible  not  to  overstep  the 
addition  of  soda,  for  the  pink  colour  produced  in  any  case  will  be 
only  slight.  Neglect  the  number  of  c.c.  of  soda  solution  used,  as 
their  purpose  is  only  to  neutralize  the  liquid.  Add  to  the  hot 
solution  half  its  present  bulk  of  glycerine;  the  pink  colour  will 
disappear.  Add  from  a  burette  decinormal  soda  solution  till  a 
pink  colour  reappears.  Note  only  the  number  of  c.c.  used  in 
this  latter  step,  and  from  them  calculate  the  quantity  of  boric 
acid  present  by  multiplying  the  number  of  c.c.  by  0-0062.  This 
will  give  the  total  boric  acid  and  borax  in  terms  of  H3BO3.  In 
the  case  of  butter,  10  to  20  grammes  should  be  washed  (after 
0*5  c.c.  of  normal  H  SO4  is  added)  in  a  separating  funnel  with 
three  successive  quantities  of  hot  water,  these  washings  being 
allowed  to  flow  out  into  a  small  flask.  The  contents  of  this  flask 
are  to  be  titrated  just  as  for  milk  or  cream,  first  adding  decinormal 
NaHO  till  a  faint  pink  colour  appears,  then  adding  glycerine 
and  titrating  with  the  NaHO. 

If  boric  acid  has  been  added  to  milk,  it  cannot  be  detected  as 
free  boric  acid  after  about  two  days,  as  by  that  time  it  combines 
with  the  lime-salts  of  the  milk. 

To  test  for  boric  acid  in  meat,  mince  the  meat  and  warm 


CHEMICAL   ANTISEPTICS    IN    FOOD  375 

with  about  an  equal  bulk  of  distilled  water  acidified  with  hydro- 
chloric acid,  for  half  an  hour;  the  liquid  is  then  decanted, 
filtered,  evaporated  to  dryness,  the  solid  residue  aslicd,  and  the 
aqueous  extract  of  the  ash,  slightly  acidified  with  hydrochloric 
acid,  is  tested  by  turmeric  paper. 

The  distillate  obtained  by  boiling  the  minced  meat  would 
also  furnish  evidence  of  traces  of  formic  aldehyde  (if  such  are 
present)  if  a  drop  of  milk  be  added  to  the  distillate  and  the 
mixture  exposed  to  Hehner's  test  (see  below) . 

For  a  close  estimation  of  boric  acid,  50  grammes  of  the  meat 
are  incinerated  (complete  combustion  is  not  essential),  transferred 
to  a  short-necked  flask,  and  acidified  with  hydrochloric  acid.  A 
little  solid  calcium  chloride  is  added,  and  the  whole  distilled  in 
a  current  of  methyl-alcohol  until  the  distillate  no.  longer  contains 
boric  acid.  If  calcium  chloride  is  not  added,  a  considerable 
amount  of  boric  acid  will  be  retained  in  the  distilling  flask.  The 
flask  is  connected  with  a  condenser,  and  four  or  five  portions  of 
20  c.c.  each  of  methyl- alcohol  are  distilled  (by  means  of  a  calcium 
chloride  bath)  into  sodium  hydroxide.  The  distillate  is  evapor- 
ated to  dryness  to  expel  the  methyl-alcohol,  care  being  taken 
that  it  is  distinctly  alkaline;  the  residue  is  dissolved  in  20  c.c. 
of  water  acidified  with  hydrochloric  acid,  heated  to  the  boiling- 
point  to  expel  carbonic  acid,  and  the  boric  acid  is  then  estimated 
in  the  manner  described  on  the  preceding  page. 

Formaldehyde.— 'By  heating  a  solution  containing  this  anti- 
septic small  amounts  may  often  be  detected  in  the  odour  given 
off.  In  milk  it  is  mostly  or  entirely  gone  in  three  days,  and  it 
is  always  greatly  reduced  in  forty-eight  hours. 

Hehner's  test  is  to  float  the  milk  on  H2SO4  (go  to  94  per  cent.) 
in  a  test-tube;  a  slight  greenish  tinge  forms  at  the  junction  of 
the  two  liquids  if  formic  aldehyde  is  absent;  but  a  violet  ring, 
if  present.  The  colour  is  permanent  for  three  days.  If  milk  be 
first  diluted  with  an  equal  bulk  of  water,  the  delicacy  of  the  test 
is  increased. 

Hehner  states  that  the  reaction  depends  upon  the  presence  of 
casein,  and  that  is  the  reason  for  adding  a  drop  of  milk  to  wine, 
vinegar,  etc.  The  commercial  acid  should  be  employed,  as  the 
acid  should  contain  a  trace  of  ferric  salt  as  impurity.  The 
addition  of  a  little  beef-peptone  increases  the  delicacy  of  the  test. 
The  test  is  unsatisfactory  in  the  presence  of  hydrogen  peroxide, 
but  then  positive  results  may  be  obtained  after  removing  the 


376  LABORATORY    WORK 

H2O2  by  means  of  reducing  agents.  A  delicate  means  of  testing 
is  to  examine  the  first  portions  of  the  distillate,  when  the  article 
is  liquid  (such  as  milk,  wine,  etc.). 

Ta  test  wine  or  vinegar,  add  a  drop  of  milk  to  the  sample, 
and  then  pour  the  mixture  on  to  H2SO4;  a  blue  ring  forms  if 
formic  aldehyde  is  present,  but  not  so  with  only  ordinary  alde- 
hyde. 

To  test  butter,  examine  the  aqueous  liquor  which  separates 
when  the  butter  is  melted. 

Dr.  G.  W.  Monier-Williams  reported  (191 2)  to  the  Local 
Government  Board  upon  the  subject  of  a  new  preservative 
("  m3'stin  ")  which  had  been  found  in  milk.  The  substance 
consisted  of  a  mixture  of  formaldehyde  and  sodium  nitrite,  and 
the  effect  of  adding  the  sodium  nitrite  was  to  prevent  the 
Hehner  reaction  from  indicating  the  presence  of  formaldeltyde. 
The  "  mystin"  may,  however,  be  detected  by  distilling  over  the 
formaldehyde  from  the  milk,  and  by  applying  the  Griess-Ilosvay 
test  for  nitrites. 

The  following  test  for  formaldehyde  is  in  use  in  the  laboratory 
of  the  State  Board  of  Health,  Massachusetts:  10  c.c.  of  hydro- 
chloric acid  (specific  gravity  i"2)  are  added  to  an  equal  amount 
of  milk  in  a  porcelain  dish.  A  drop  of  dilute  ferric  chloride 
solution  is  added,  and  the  mixture  heated  to  just  below  the 
boiling-point  and  vigorousl}^  stirred.  The  presence  of  formalin 
is  indicated  by  a  violet  coloration,  varying  in  depth  with  the 
amount  present. 

An  approximate  estimation  may  be  made  (Liverseege)  as 
follows:  The  reagent  consists  of  a  mixture  of  100  c.c.  of  sulphuric 
acid  and  2*5  c.c.  of  normal  ferric  chloride,  which,  as  already 
indicated,  causes  the  formation  of  a  violet-blue  ring  when  added 
to  milk  containing  formaldehj'de.  Ten  c.c.  of  the  suspected 
sample  are  put  into  a  25  c.c.  stoppered  cylinder,  and  the  reagent 
is  added  (i  c.c.  at  a  time)  until  a  violet  colour  appears  and  does 
not  increase  in  intensity.  By  making  experiments  side  by  side 
with  samples  containing  a  definite  proportion  of  formaldehyde, 
a  fair  idea  as  to  the  percentage  ma}^  be  obtained,  as  the  more 
formaldehyde  is  present,  the  sooner  the  violet  colour  forms. 

W.  Scott  Tebb  suggests  another  useful  method  of  making  a  very 
approximate  colorimetric  estimation  of  formic  aldehyde.  The 
method  depends  on  the  pink  colour  which  develops  when  fuchsin 
decolorized  with  a  saturated  solution  of  sulphurous  acid  (Schiff' s 


CHEMICAL    ANTISEPTICS    IN    FOOD  377 

reagent)  is  added  to  the  clear  filtrate  obtained  after  the  separa- 
tion (by  means  of  acid)  of  casein  and  fat  from  diluted  milk. 

Fifty  CO.  of  the  clear  hltratc  from  the  milk  are  poured  into  a 
Nessler  glass,  5  c.c.  of  vSchiff's  reagent  are  added,  and  the  mixture 
is  allowed  to  stand  for  ten  minutes.  In  estimating  small  traces 
of  formaldehyde,  which  may  readily  be  done  if  the  Schiff's  reagent 
is  sufficiently  sensitive,  it  is  advisable  to  allow  the  liquid  to  stand 
for  a  longer  period — that  is  to  say,  for  half  an  hour  or  even  an 
hour.  To  estimate  the  exact  percentage  of  the  formaldehyde 
a  number  of  standards  must  be  prepared  of  known  amounts  of 
formalin  added  to  milk.  Each  standard  is  treated  by  precipi- 
tation, filtration,  etc.,  in  precisely  the  same  manner  as  the  milk 
under  examination.  The  Schiff's  reagent  is  then  added,  and  the 
colour  of  the  sample  in  the  Nessler  glass  is  matched  with  the 
nearest  standard.  In  ordinary  milk  adulteration  from  0-002  to 
o-oi  per  cent,  of  formaldehyde  may  be  expected,  and  eight  stan- 
dards, containing  0-002  per  cent.,  o-oi  per  cent.,  and  six  inter- 
mediate percentages,  should  be  made  up. 

Legler's  method,  as  modified  by  A.  G.  Craig,  is  satisfactory. 
The  requisites  to  the  determination  are  a  normal  solution  of 
sulphuric  acid,  an  approximately  normal  solution  of  ammonia 
(the  exact  strength  being  immaterial),  and  a  methyl-orange 
solution;  3-ounce  bottles  with  smooth  sides  and  clos'-^fitting 
soft-rubber  stoppers,  and  a  boiler  in  which  they  may  be  immersed 
to  the  neck.  Place  25  c.c.  of  the  ammonia  solution  in  each 
bottle,  but  to  one-half  of  them  add  a  sample  of  milk  containing 
0-5  gramme  of  formaldehyde.  Stopper  tightly,  place  the  bottles 
in  the  boiler,  fill  with  water  to  the  neck,  and  boil  for  one  hour. 
Cool  slowly,  and  titrate  carefully  with  sulphuric  acid  and  methyl- 
orange  to  the  first  indication  of  a  colour  change.  From  the 
differences  between  the  readings,  the  ammonia  consumed  in 
normal  cubic  centimetres  may  be  calculated;  every  c.c.  =  o-o6oi 
gramme  of  formaldehyde. 

The  errors  in  the  Legler  method  do  not  counterbalance  one 
another,  the  tendency  being  toward  low  results.  A  blank  deter- 
mination is  necessary,  and  in  the  titration  an  accurate  end-point 
is  very  important.     Any  acid  present  must  be  also  accounted  for. 

Schuch  tested  several  methods  as  to  their  suitability  for  the 
detection  of  formaldehyde  in  wines  and  in  presence  of  acetalde- 
hyde.  The  best  process  is  that  of  Arnold  and  Mentzel.  Three 
hundred  c.c.  of  wine  are  distilled  untU  10  c.c.  have  passed  over; 


37^  LABORATORY   WORK 

then  5  c.c.  are  shaken  with  1-5  c.c.  of  a  sohition  of  phenylhydra- 
zine  hydrochloride  (i  :  50),  and  4  drops  of  ferric  chloride  and  12 
■drops  of  sulphuric  acid  arc  added.  In  the  presence  of  formalde" 
hyde;  a  rose  or  dark  red  coloration  is  formed. 

When  meat  is  exposed  to  the  vapour  of  formic  aldehyde  a 
material  degree  of  penetration  ensues. 

In  testing  for  fonnaldehyde  in  meat,  10  grammes  of  minced 
meat  may  be  heated  for  five  minutes  (on  a  boiling-water  bath) 
with  water  to  every  10  c.c.  of  which  have  been  added  2  c.c.  of 
a  I  per  cent,  solution  of  phenylhydrazine  hydrochloride.  After 
heating,  the  liquid  is  cooled  and  filtered  from  the  coagulum 
through  a  loose  plug  of  cotton-wool.  To  12  c.c.  of  the  filtrate 
are  added  i  c.c.  of  5  per  cent,  potassium  ferri-cyanide  solution 
and  4  c.c.  of  concentrated  hydrochloric  acid  for  each  12  c.c.  of 
water  and  phenylhydrazine  reagent  employed  in  the  test.  By 
comparison  of  the  colour  with  standards  made  from  standard 
formaldehyde  solutions,  the  amount  of  formaldehyde  in  any 
given  meat  sample  may  be  estimated. 

Salicylic  Acid  and  Salicylates. — If  milk  is  to  be  tested,  take 
50  c.c.  and  dilute  it  with  50  c.c.  of  %vater,  then  add  5  drops  of 
acetic  acid  and  5  drops  of  a  solution  of  oxide  of  mercury  in 
nitric  acid,  and  well  shake.  After  the  albumen  is  coagulated, 
the  mixture  is  filtered.  The  clear  filtrate  is  then  shaken  w^ith 
50  c.c.  of  equal  parts  of  ether  and  light  petroleum,  and  the 
ether  is  subsequently  allowed  to  separate  out.  Draw  off  the 
ether,  place  it  in  a  clean  vessel,  and  evaporate  to  dryness. 
The  residue  dissolved  in  a  few  drops  of  hot  water  and  tested  with 
2  drops  of  a  I  per  cent,  solution  of  ferric  chloride  gives  a  violet 
or  purple  colour  in  the  presence  of  salicylic  acid. 

The  amount  may  be  very  approximately  determined  b}^  match- 
ing the  colour  produced  with  a  standard  solution  of  salicylic 
acid  (0-05  per  cent,  salicylic  acid  in  50  per  cent,  alcohol)  to 
which  2  drops  of  the  iron  solution  are  added.  In  the  quantita- 
tive estimation  S.  Harvey  recommends  the  employment  of  an 
iron-alum  solution  (i  per  cent.),  instead  of  ferric  chloride,  as  the 
colour  struck  is  purer,  deeper,  and  more  permanent;  and  Allan 
advises  that  definite  amounts  of  salicylic  acid  should  be  added 
to  a  liquid  of  the  same  kind  as  that  in  which  the  acid  is  to  be 
determined,  so  that  the  error  of  experiment  may  be  ascertained. 
Distilled  water  must  be  used  in  all  the  dilutions,  as  the  salts  of 
the  alkaline  earths  affect  the  violet  tint. 


CHEMICAL    ANTISEPTICS    IN    FOOD  379 

To  test  for  salicylic  acid  in  beer  or  wine,  the  liquid  should  be 
acidulated  with  sulphuric  acid  and  well  shaken  with  an  equal 
amount  of  a  mixture  of  ether  and  petroleum  naphtha;  let  stand, 
and  then  pipette  off  the  ethereal  layer  and  evaporate  down  to  a 
few  c.c. ;  add  a  little  water  and  a  few  drops  of  dilute  ferric  chloride 
solution  and  filter,  when  the  filtrate,  in  the  presence  of  salicylic 
acid,  will  be  of  a  violet-purple  colour.  Or  the  liquid  may  be 
distilled,  when  the  acid  will  chiefly  be  found  in  the  last  fraction 
of  the  distillate,  which  should  be  tested  with  the  ferric  chloride. 

A  trace  of  salicylic  acid  (like  citric  acid)  appears  to  be  occa- 
sionally a  natural  constituent  of  genuine  wine,  and  it  has  there- 
fore been  proposed  that  no  more  than  2  ounces  of  wine  should 
be  taken  for  the  purpose  of  testing  for  the  addition  of  the  pre- 
servative. The  trace  naturally  present  in  wines  appears  to  be 
about  0-00 1  gramme  per  litre. 

Benzoic  Acid  and  Benzoates. — C.  Revis  recommends  the 
following  procedure  for  testing  for  the  presence  of  benzoic  acid 
in  milk,  and  the  writer  finds  it  very  satisfactory : 

One  hundred  c.c.  (not  less)  of  milk  are  diluted  with  an  equal 
volume  of  water,  and,  after  the  addition  of  5  c.c.  of  10  per  cent, 
sodium  carbonate  solution,  heated  in  boiling  water  for  two  to 
three  minutes;  10  c.c.  of  20  per  cent,  calcium  chloride  solution 
are  then  added,  and  the  heating  continued,  until  coagulation  of 
the  casein,  etc.,  is  complete.  The  liquid  is  then  cooled  and  fil- 
tered, and  the  filtrate  neutralized  with  hydrochloric  acid,  to 
litmus-paper.  Ten  c.c.  of  Fehling  copper  sulphate  solution  (not 
mixed  with  the  tartrate  solution),  followed  by  10  c.c.  of  a  solu- 
tion of  potassium  hydrate  (containing  31 'iS  grammes  per  litre) 
are  now  added,  and  the  liquid  again  filtered.  The  filtrate  is 
poured  into  a  separating  funnel,  acidified  with  hydrochloric  acid, 
and  extracted  with,  about  50  c.c.  of  ether.  The  ether  is  then 
washed  three  times  with  a  little  distilled  water.  About  10  c.c. 
of  water  are  now  added  to  the  ether  in  the  funnel,  together  with 

1  drop  of  phenolphthalein  solution,  and  then  a  saturated  solution 
of  barium  hydrate  added  gradually,  until,  on  violent  shaking, 
the  aqueous  layer  remains  pink;  this  is  then  filtered  off  into  a 
porcelain  basin  and  evaporated  to  about  5  c.c.  The  contents  of 
the  basin  are  filtered  into  a  test-tube  and  dilute  (i  in  100)  acetic 
acid  dropped  in  until  the  pink  colour  is  discharged,  after  which 

2  more  drops  are  added.  The  liquid  is  then  tested  with  i  drop 
of  10  per  cent,  neutral,  freshly  prepared  solution  of  ferric  chloride, 


380  LABORATORY   WORK 

when,  in  the  presence  of  benzoic  acid,  a  fine  reddish-yellow 
precipitate  forms.  This  method  will  detect  0-02  per  cent,  of 
benzoic  acid.  When  testing  cream,  50  c.c.  are  diluted  to  200  c.c. 
with  distilled  water,  and  the  mixture  is  treated  as  directed  above. 

Saccharin. — One  hundred  c.c.  of  the  material  is  acidified  with 
dilute  sulphuric  acid  (i  in  4),  and  extracted  with  a  mixture  of 
equal  parts  of  ether  and  light  petroleum.  The  ethereal  extract 
is  then  drawn  off  and  evaporated  at  a  gentle  heat,  when  the 
residue  will  have  a  sweet  taste  if  saccharin  is  present.  Two  c.c. 
of  a  saturated  solution  of  sodic  hydrate  are  then  added,  and 
heat  applied  until  the  residue  dries  and  the  mass  fuses.  The 
heat  is  maintained  for  half  an  hour,  when  the  saccharin  is  con- 
verted into  salicylic  acid.  The  residue  is  acidulated  with  dilute 
sulphuric  acid,  and  the  ferric  chloride  test  applied.  If  salicylic 
acid  is  originally  present,  it  may  be  removed  by  dissolving  the 
residue  from  the  ether  extract  in  50  c.c.  of  dilute  hydrochloric 
acid,  adding  bromine  water  to  excess,  well  shaking  and  filtering. 

Should  the  ether  extract  contain  benzoic  acid  in  addition  to 
saccharin,  the  extract  may  be  heated  at  110°  to  iis"^  C.  until 
the  whole  of  the  benzoic  acid  has  sublimed,  the  saccharin  re- 
maining unchanged. 

Sulphurous  Acid  and  Sulphites. — If  beer  or  wine  is  mixed 
with  hydrochloric  acid,  and  granulated  zinc  is  added  to  the  small 
flask  containing  the  liquid,  a  lead  acetate  paper  placed  over  the 
mouth  of  the  flask  becomes  discoloured  (SOg  +  3H2=  SH2  -l-  2H2O) . 

For  a  quantitative  estimation,  add  5  c.c.  of  phosphoric  acid  to 
200  c.c.  of  wine  or  beer,  and  distil  100  c.c.  in  a  current  of  CO2, 
receiving  the  distillate  into  20  c.c.  of  decinormal  iodine  solution. 
After  the  distillate  has  been  collected,  the  iodine  solution  must 
still  be  coloured  [i.e.,  must  contain  some  free  iodine),  or  the 
experiment  must  be  repeated  with  more  of  the  iodine  solution. 

The  sulphurous  acid  liberated  by  the  phosphoric  acid  is 
oxidized  to  sulphuric  acid  (S02  +  2H20-l-l2=  H2S04-f-2HI),  and 
the  sulphuric  acid  in  the  distillate  may  be  precipitated  by  HCl 
and  BaCl2  as  BaS04.  One  milligramme  of  BaS04=  0*274  milli- 
gramme SO2. 

Or  the  following  simple  method  may  be  employed:  25  c.c.  of 
normal  potash  solution  are  added  to  50  c.c.  of  the  sample,  and 
the  mixture  is  shaken  occasionally  for  fifteen  minutes.  Ten  c.c. 
of  25  per  cent,  sulphuric  acid  and  a  little  starch  solution  are  then 
added,  and  the  mixture  is  rapidly  titrated  with  decinormal  iodine 


CHEMICAL   ANTISEPTICS   IN    FOOD  30I 

solution  until  a  blue  tint  remains  for  a  few  minutes.  Each  c.c. 
of  iodine  solution  required  x  0-00127  =  ^^2  ^^  grammes  per 
100  c.c. 

Sulphites  in  meat  may  be  tested  for  by  taking  100  grammes  of 
the  finely  ground  meat  and  making  a  thin  suspension  with  water; 
acidify  with  phosphoric  acid;  then  distil,  and  collect  distillate 
in  a  few  c.c.  of  distilled  water,  to  which  add  a  few  drops  of 
bromine  water  and  boil;  then  add  a  little  barium  chloride  solu- 
tion, when  a  white  precipitate  will  indicate  SOg- 

The  amount  of  sulphites  recoverable  on  analysis  falls  far  short 
of  that  originally  present. 

Fluorides  are  used  as  preservatives  for  sweet  wines  and  beer, 
and  more  rarely  for  milk,  butter  and  meat.  A  little  ammonium 
carbonate  is  added  to  100  grammes  of  the  material  so  as  to 
render  it  slightly  alkaline;  it  is  then  brought  to  the  boiling-point. 
A  few  c.c.  of  calcium  chloride  solution  are  added,  and  the  boiling 
continued  for  ten  minutes.  The  precipitate  is  collected,  washed , 
dried,  and  ignited.  When  cold,  a  few  drops  of  strong  sulphuric 
acid  are  added,  and  the  dish  is  covered  with  a  piece  of  glass 
partly  covered  on  its  under  surface  with  paraffin.  The  dish 
is  then  heated  over  warm  water  for  one  hour,  when  the 
glass  will  be  etched  if  fluorides  are  present.  Small  quantities 
can  only  be  discovered  by  working  on  large  amounts  of  the 
material. 

Hydrogen  Peroxide. — This  powerful  oxidizing  agent  has  been 
suggested  by  Budde  as  a  harmless  means  of  preserving  milk 
and  cream.  To  10  c.c.  of  milk  sample  add  i  c.c.  of  i  per  cent, 
ortol  solution  (freshly  made),  when,  in  presence  of  hydroxyl, 
a  dull  crimson  colour  is  produced,  unless  the  milk  has  been 
heated  above  72°  C,  when  the  addition  of  a  little  fresh  milk 
is  required.  Paraphenylenediamine  similarly  gives  a  blue 
coloration.  In  the  presence  of  organic  matter  hydroxyl  splits 
up  slowly  into  water  and  free  oxygen,  and  so,  after  six  to  eight 
hours,  will  not  be  found. 

Schryver  suggests  a  physico-chemical  method  for  estimating 
antiseptic  values.  The  principle  of  the  method  consists  in  the 
determination  of  the  inhibition  of  the  rate  of  putrefaction  of  a 
given  mixture  from  the  presence  of  varying  quantities  of  anti- 
septic, as  indicated  by  the  rate  of  chemical  change  of  this  mixture. 
For  this  purpose  a  solution  of  5  per  cent,  gelatine  and  i  per  cent, 
peptone  infected  by  fgeces  may  be  employed.     As  putrefactive 


382  LABORATORY   WORK 

bacteria  break  down  tlie  gelatine,  an  alteration  in  the  physical 
properties  of  the  mixtnre  leads  to  an  altered  degree  of  electrical 
conductivit}',  which  may  be  measured. 

The  Colouring  Agents  employed  in  Food. 

The  question  of  the  detection  and  identification  of  artificial 
colouring  matters  in  articles  of  food  is  of  considerable  importance 
to  the  food  analyst  in  view  of  the  ever-increasing  use  of  the 
aniline  and  other  synthetic  dyes,  some  at  least  of  which  cannot 
but  be  regarded  as  objectionable. 

Harmful  Colouring  Agents. — Those  formerly  employed  were 
mostly  of  mineral  origin,  but  at  the  present  day  the  sulphate  of 
copper  affords  practically  the  sole  important  instance  of  the  use 
of  mineral  agents  in  the  coloration  of  food  {vide  pp.  363,  364). 

Gamboge  and  picric  acid  are  said  to  be  occasionally  used  for 
the  production  of  a  yellow  colour. 

Gamboge  is  very  insoluble  in  water,  but  readily  so  in  alcohol. 
Its  presence  is  detected  by  dissoh-ing  out  the  colouring  matter 
from  the  article  by  alcohol,  filtering,  and  then,  when  water  is 
added,  the  gamboge  resin  is  precipitated;  this  precipitate  will 
dissolve  in  ammonia  with  the  production  of  a  blood-red  colour. 

Picric  acid  (tri-nitro-phenol)  can  be  extracted  by  alcohol  and 
ether;  it  is  detected  by  drying  on  the  water-bath  after  the 
addition  of  a  solution  of  the  cyanide  of  potassium  and  caustic 
potash,  when  the  blood-red  colour  of  the  iso-purpurate  of  potas- 
sium forms. 

Certain  aniline  colours  are  liable  to  contain  arsenic,  as,  for  ex- 
ample, in  the  production  of  rose  aniline  arsenic  acid  is  used  as  an 
oxidizing  agent,  and  crude  oil  of  vitriol  may  have  been  employed 
in  the  manufacture  of  other  dyes;  but  if  tested  and  found  to 
be  free  from  this  metal,  they  are  mostly  harmless.  Some,  how- 
ever, such  as  naphthol  green,  metanil-yellow,  Victoria  yellow, 
Martins'  yellow,  Bismarck  brown,  methylene  blue,  and  gentian 
violet  are  more  or  less  poisonous,  apart  from  the  presence  of 
arsenic.  As  a  rule,  only  minute  quantities  of  these  aniline  colours 
are  employed  at  a  time. 

To  distinguish  between  Victoria  yellow,  picric  acid,  and  Mar- 
tins' yellow,  evaporate  off  the  spirit  by  which  the  colour  was 
extracted,  and  cautiously  taste  for  the  bitter  flavour  of  picric 
acid;  then  treat  with  a  little  dilute  hydrocliloric  acid,  and  when 


COLOURING   AGENTS    EMPLOYED    IN    FOOD  383 

the  solution  has  become  nearly  decolorized,  introduce  a  piece 
of  zinc  for  about  an  hour.  Picric  acid  yields  a  fine  blue,  and 
Victoria  yellow  a  blood  red.  Martius'  yellow  gives  a  golden- 
yellow  solution  from  which  acids  separate  a  white  precipitate; 
this  is  not  the  case  with  picric  acid. 

Aniline  colours  may  be  detected  by  the  iso-nitril  test:  To  a 
little  of  the  extract  an  equal  amount  of  potash-lye  is  added, 
followed  by  2  drops  of  chloroform ;  if  the  whole  is  gently  warmed 
for  a  minute,  and  then  boiled,  the  characteristic  disagreeable 
odour  of  iso-nitril  generally  becomes  perceptible.  The  well- 
known  bleaching  solution  reaction  for  aniline  can  be  readily 
'  obtained  by  adding  an  excess  of  the  reagent  to  a  solution  of  the 
aniline  in  water. 

Aniline  colours  are  largely  employed.  They  are  more  readily 
soluble,  cheaper  (in  consideration  of  the  amount  employed),  and 
they  withstand  the  effect  of  light  and  time  better  than  the 
ordinary  vegetable  colours  available  for  colouring  food. 

The  various  harmless  colouring  agents  are  very  numerous, 
and  are  mostly  of  animal  and  vegetable  origin.  They  have 
almost  completely  replaced  the  harmful  colouring  agents  formerly 
used.  To  enumerate  those  which  are  most  commonly  employed 
in  the  production  of  various  tints : 

A  red,  pink,  crimson,  or  lake  colour  is  generally  produced  by 
either  cochineal  or  the  aniline  reds  (f uchsine  and  magenta) . 

The  former  colouring  agent  is  derived  from  the  cochineal 
insect,  and  is,  like  magenta,  commonly  employed.  It  can  be 
detected  by  its  character  of  turning  violet  with  alkahes  and 
yellowish-red  with  acids. 

The  reddish  colours  extracted  from  the  root  of  the  madder, 
from  beetroot,  and  from  saffiower,  are  also  used. 

The  colour  due  to  safflower  turns  light  brown  and  bleaches 
when  treated  with  concentrated  sulphuric  acid. 

Logwood  is  also  of  common  employ,  and  may  be  demonstrated 
by  extracting  with  alcohol  and  then  adding  alum  and  ammonium 
carbonate,  when  a  lavender  colour  results. 

A  yellow,  amber,  or  orange  hue  is  commonly  imparted  by 
annatto,  turmeric,  aniline  orange,  marigold  (the  extract  of  which 
yields  a  permanent  dark  olive-green  with  concentrated  sulphuric 
acid),  chrysophanic  acid  (which  is  extracted  from  rhubarb,  and 
yields  a  fine  purple  colour  with  caustic  potash) ,  and  saffron. 

Annatto  (which  is  obtained  from  the  seed  of  a  plant  named 


384  LABORATORY    WORK 

Bixa  ordlana)  is  very  extensively  used  as  a  colouring  agent, 
and  like  turmeric  and  saffron  it  is  readily  soluble  in  alcohol, 
though  not  in  water.  If  in  either  case  the  alcohol  is  subsequently 
evaporated  down  and  the  residue  touched  with  a  drop  of  concen- 
trated sulphuric  acid,  annatto  and  saffron  turn  dark  blue,  changing 
to  green,  which  in  the  case  of  saffron  turns  to  a  reddish-brown; 
and  saffron  furnishes  a  very  peculiar  odour.  Turmeric  yields  a 
violet-red,  and  will  turn  brown  with  alkalies. 

A  violet  or  bkce  colour  is  frequently  derived  from  the  use  of  the 
aniline  blues  and  violets. 

Methylene  blue  may  be  detected  by  adding  hydrochloric  acid 
to  the  extract,  when  a  greenish  precipitate  results.  Zinc  dust 
reduces  it,  but  the  colour  returns  after  exposure  to  the  air. 

Methyl-violet  extracted  and  treated  with  hydrochloric  acid 
yields  first  a  green  and  then  a  yellow  colour. 

Indigo  is  extensively  employed,  and  it  sublimes  in  dense  violet 
vapours  when  the  article  is  burned.  The  colour  is  discharged 
by  the  permanganate  of  potassium  in  the  presence  of  potash 
solution. 

The  blue  colour  of  litmus  affords  another  means  of  such 
coloration.  This  substance  is  derived  from  Rocella  tinctoria  and 
from  certain  other  lichens. 

A  purple  colour  is  usually  formed  from  a  mixture  of  blue  with 
some  vegetable  pink,  such  as  rose-pink,  logwood,  and  cochineal. 

The  various  shades  of  brown  are  most  commonly  imparted  by 
heating  sugar  to  various  stages  ("  caramel  ") ;  and  a  green  colour 
is  now  almost  invariably  obtained  by  the  use  of  the  chlorophyll 
extracted  from  plants  rich  in  this  substance,  such  as  parsley, 
spinach,  etc.     The  aniline  greens  are  also  used. 

If  the  substance  is  thoroughly  macerated  in  a  small  quantity 
of  slightly  warmed  distilled  water  and  the  colouring  matter  is 
dissolved  out  by  these  means,  and  the  coloured  solution  when 
treated  with  a  solution  of  sodium  hypochlorite  and  gently  warmed 
loses  its  colour,  then  it  is  probably  an  aniline  colour.  Most 
harmless  colouring  agents  are  soluble  in  alcohol,  ether,  or  chloro- 
form. Further,  the  ash  of  the  substance  will  furnish  no  inor- 
ganic constituents  that  are  capable  of  forming  the  colour  present. 
In  this  connection  it  should  be  noted  that  metallic  mordants 
have  been  used  for  fixing  organic  colours. 

If  the  colour  is  insoluble  in  water  and  not  bleached  by  sodium 
hypochlorite,  it  is  in  all  probability  of  mineral  origin,  and  the 


COLOURING   AGENTS   EMPLOYED    IN   FOOD  385 

presence  of  copper,  zinc,  lead,  chromium  and  arsenic  should  at 
least  be  tested  for.  Such  tests,  in  many  cases,  are  best  made 
from  a  solution  of  the  ash  of  the  substance. 

Almost  all  the  azo-dyes,  now  so  largely  in  use,  are  decolorized 
by  stannous  chloride  in  an  aqueous  solution  containing  hydro- 
chloric acid. 

Araia's  wool-test  is  valuable.  White  wool  is  cleansed  by 
boiling  for  a  few  minutes  with  caustic  soda,  and  then  thoroughly 
washing  with  water  to  remove  all  alkah.  About  100  c.c.  of  the 
liquid  or  extract  is  mixed  with  i  per  cent,  of  potassium  acid 
sulphate,  and  raised  to  the  boiling-point.  The  wool  is  then 
soaked  in  the  liquid  for  several  minutes,  removed,  well  washed  in 
boiling  water,  and  dried.  Many  of  the  artificial  colours  dye  the 
wool,  and  the  dye  is  either  not  changed  by  ammonia  solution, 
or,  if  changed,  is  restored  by  further  washing  with  water.  The 
natural  colouring  matter  of  wines,  fruits,  cane-sugar,  etc.,  is 
not  taken  up  by  the  wool,  and  any  sHght  colour  which  may 
be  taken  up  is  changed  by  ammonia,  and  is  not  restored  by 
washing. 

Meats  (especially  sausage  meats)  may  be  coloured,  and  coal- 
tar  colours  are  mostly  employed.  Water  or  alcohol  will  extract 
sufficient  for  the  wool-test. 

A  simple  test  for  added  colouring  matter  in  milk  is  to  let  it 
stand.  In  the  case  of  genuine,  high-coloured  milk  most  of  the 
colour  rises  with  the  cream,  but  the  bulk  of  any  artificial  colour- 
ing matter  generally  remains  in  the  milk.  A  simple  test  for 
the  coal-tar  dyes  employed  in  milk  is  the  addition  of  hydro- 
chloric acid  to  the  fresh  milk,  when  a  pink  colour  forms  in  their 
presence. 

The  use  of  any  dye,  harmless  or  otherwise,  to  colour  food  in 
order  to  conceal  damage  or  inferiority  should  be  prohibited. 
Certainly  it  should  be  illegal  to  colour  milk. 

Dirt  in  Food. — ^This  may  be  defined  as  adventitious  matter 
foreign  to  the  special  article  of  food  under  consideration,  and 
derived  in  various  ways  during  collection  or  manufacture,  while 
exposed  for  sale,  during  transit  to  the  retailer  and  consumer, 
and  while  in  the  hands  of  the  consumer. 

The  microscopic  characters  of  the  dirt  which  gains  access  to 
milk  has  already  been  indicated,  and  such  an  examination  of 
other  articles  of  food  often  discloses  the  presence  of  cl^y  and 
sand,  soot,  straw,  hair,  wool  and  cotton  fibres,  sawdust,  vegetable 

25 


386  LABORATORY   WORK 

matter,  and  motile  organisms  belonging  to  the  infusoria. 
Bacteriologically  the  liquefying  bacilli  largely  predominate. 

As  would  be  expected,  the  amount  of  dirt  found  varies  greatly 
even  in  different  samples  of  the  same  material.  In  such  articles 
as  watercress,  parsley,  apples,  tomatoes,  cheriies  and  grapes, 
currants  and  dates  (exposed  on  stalls),  sugar  and  salt,  black 
pepper,  the  writer  and  Dr.  Dove  found  dirt  varying  from  I  grain 
to  over  300  grains  per  pound. 

Dirt  containing  micro-organisms,  moulds,  yeast,  etc.,  may  do 
considerable  harm  to  the  food  itself,  setting  up  fermentation, 
destroying  its  keeping  powers,  and  thus  making  it  unmarketable 
or  unwholesome.  Furthermore,  the  knowledge  that  food  has 
been  placed  under  uncleanly  conditions  is  unappetizing,  and 
there  is  always  the  danger  involved  in  such  dirty  handling  and 
storing  that  it  may  get  contaminated  by  germs  of  communicable 
disease.  Although  this  danger  is  not  great  in  most  articles  of 
food,  it  is  considerable  in  such  an  article  as  milk. 


CHAPTER  XV 

ARSENIC  IN  FOOD— ARSENIC  AND  OTHER  POISONOUS 
METALS  IN  WALL-PAPERS,  ETC.— RAG   FLOCK 

It  will  frequently  happen  that  the  metal  under  examination  is 
distributed  in  solid  organic  matter;  in  these  cases  it  is  necessary 
to  destroy  the  organic  matter  before  proceeding  to  test  for  metallic 
impurities. 

There  are  several  alternative  methods  of  separating  organic 
matter  from  inorganic : 

1.  The  organic  matter  may  be  destroyed — 

(a)  By  careful  ignition.  But  by  this  means  some  of  the 
inorganic  matter  is  apt  to  be  lost.  In  addition  to  the 
losses  indicated  on  p.  2 — i.e.,  when  the  solid  residue 
of  a  water  is  ignited — arsenic  and  antimony  may 
escape,  and  copper,  mercury  and  zinc  may  suffer 
partial  volatilization.  (The  addition  of  concentrated 
sulphuric  acid  before  ignition  would,  by  forming  copper 
and  zinc  sulphates,  prevent  any  volatilization  of  those 
metals.) 

(&)  By  heating  with  oxidizing  agents,  such  as  a  mixture 
of  chlorate  of  potassium  and  hydrochloric  acid. 

(c)  The  organic  matter  may  be  destroyed  by  Kjeldahl's 
process. 

2.  The  colouring  or  organic  matter  may  sometimes  be  separ- 
ated by  filtration  or  dialysis. 

Arsenic  in  Food. 

Of  substances  which  are  subject  to  risk  of  such  contamina- 
tion the  majority  are  those  in  which  glucose  is  used,  or  which 
(hke  glucose)   are  prepared    by  the  use   of    a  relatively  large 

387 


388  LABORATORY   WORK 

amount  of  sulphuric  or  hydrochloric  acid,  which  so  generally 
contain  arsenic. 

Traces  of  arsenic  have  been  found  in  jams,  sweets,  lemonade, 
liqueurs,  sugar,  glycerine  and  treacle — all  now  largely  manu- 
factured from  glucose — and  also  in  sulphate  of  sodium,  phosphate 
of  sodium,  carbonate  of  sodium  and  potassium,  caustic  soda, 
sulphurous  acid,  sulphites,  borax,  oxide  of  iron  (used  for  colour- 
ing confectionery),  etc.  It  has  also  been  pointed  out  that  the 
coke  used  for  kilning  barley  in  the  preparation  of  beer  may  give 
off  traces  of  arsenic  when  burned. 

Traces  of  arsenic  may  gain  admission  to  food  even  in  the  process 
of  cooking,  from  the  enamelled,  etc.,  cooking  utensils  emploj'ed. 

Traces  are  also  to  be  found  in  the  ash  of  many  of  the 
natural  foods,  and  notably  such  vegetables  as  cabbages,  turnips, 


FIG.  S3. CRYSTALS  OF  ARSENIOUS  ACID. 

potatoes,  spinach,  haricots,  peas,  and  lentils.  It  is  not  surpris- 
ing, therefore,  that  Gautier  and  Bernand  find  that  arsenic  exists 
normally  in  men  and  animals. 

The  Royal  Commission  on  Arsenical  Poisoning  suggested  that 
action  should  be  taken  under  the  Sale  of  Food  and  Drugs  Acts 
when  any  liquid  is  found  to  contain  y—  of  a  grain  or  more  of 
arsenic  in  the  gallon ;  or  when  any  solid  contains  ^i^y  grain  of 
arsenic  or  more  in  the  pound. 

The  method  (Reinsch)  of  examining  beer  for  arsenic,  which 
was  recommended  in  1900  by  a  strong  committee  of  chemical 
experts,  is  as  follows: 

Two  hundred  c.c.  of  the  beer  are  heated  to  boiling  in  a 
porcelain  dish,  30  c.c.  of  pure  hydrochloric  acid  are  added,  and 
then  a  piece  of  clean,  bright  copper-foil,  |-  inch  by  J  inch  in  size ; 
the  boiling  is  continued  for  forty-five  minutes,  the  water  lost  by 
evaporation  being  replaced.  If  after  that  time  the  copper  re- 
mains bright,  no  arsenic  is  present.  If  a  deposit  has  been  formed, 
the  foil  is  washed  successively  with  water,  alcohol,  and  ether, 
dried  at  100^  C,  and  heated  in  a  2-inch  reduction-tube — the 
upper  part  of  which  should  be  previously  warmed.  If  any  sub- 
limate is  obtained,  it  must  be  examined  under  a  magnifying 


ARSENIC   IN    FOOD  3^() 

power  of  200  diameters,  when,  if  arsenical,  octahedral  and 
tetrahedral  crystals  will  be  seen.  Perfect  octahedra  are  com- 
paratively rare,  the  majority  of  the  crystals  being  modified 
forms  of  the  octahedron  or  tetrahedron.  In  the  case  of  very 
faint  sublimates  the  crystals  have,  as  a  rule,  the  appearance  of 
minute  triangles. 

Sulphites  of  various  kinds  are  often  added  to  beer  in  small 
quantity  as  preservatives,  and  when  present  they  cause  the 
formation  of  black  copper  sulphide.  This  stain,  however,  re- 
mains unchanged  when  the  copper  is  heated  in  the  small  tube, 


FIG.    84. marsh's    apparatus    FOR    TESTING    FOR    ARSENIC. 


and,  of  course,  it  furnishes  no  sublimate.  Occasionally  a  slight 
film  of  organic  matter  diminishes  the  brightness  of  the  copper, 
but  this  again  could  not  possibly  be  mistaken  for  arsenic. 

Allen  advises  that  the  operator  should,  as  a  preliminary  treat- 
ment to  eliminate  sulphites,  add  hydrochloric  acid  and  a  little 
bromine  water,  and  boil  the  liquid  for  a  few  minutes.  To  obviate 
the  difficulty  caused  by  the  fact  that  arsenic  acid  only  responds 
to  Reinsch's  test  after  prolonged  boiling,  and  in  presence  of  much 
acid,  he  adds  a  little  solution  of  cuprous  chloride  in  hydrochloric 
acid,  which  reduces  the  arsenic  to  the  arsenious  condition. 

A  joint  committee  of  the  Society  of  Chemical  Industry  and 
of  the  Society  of  Public  Analysts  reported  (igoi)  in  favour  of 
Marsh's  process. 

In   the   horizontal   drying-tube   of   the    apparatus   shown    in 


390  LABORATORY   WORK 

Fig.  84  a  roll  of  blotting-paper  soaked  in  lead  acetate  solntion 
and  dried  is  first  placed,  then  a  wad  of  cotton-wool,  then 
granulated  calcium  chloride,  and  finally  a  thick  wad  of  cotton- 
wool. 

Mode  of  Testing  Recommended. — The  HCl  employed  must 
always  first  be  iiced  from  the  usual  traces  of  arsenic.  To  effect 
this  it  is  well  to  add  bromine  and  an  excess  of  sulphurous  acid  to 
it,  and  to  distil  off  and  reject  about  one-fifth,  the  remainder  of 
the  distillate  being  generally  quite  free  from  arsenic,  even  if 
crude  yellow  hydrochloric  acid  has  been  employed.  About 
20  grammes  of  zinc  are  placed  in  the  bottle,  after  washing  with 
water  to  remove  particles  of  dust  which  may  contain  arsenic; 
all  parts  of  the  apparatus  are  connected,  and  a  sufficient  quantity 
of  hydrochloric  acid  allowed  to  flow  from  the  funnel,  so  as  to 
cause  a  fairly  brisk  evolution  of  hj^drogen.  When  the  hydrogen 
flame  burns  with  a  round  (not  pointed)  tip,  all  air  has  been  re- 
moved from  the  apparatus.  The  Bunsen  burner  should  then  be 
placed  under  the  hard  glass  tube  as  shown  in  the  figure,  and  more 
acid  (10  to  20  cc  is  generally  enough)  run  in.  With  pure  materials 
no  trace  of  a  mirror  is  obtained  in  the  contracted  part  of  the  tube 
just  beyond  the  flame,  in  half  an  hour.  Great  care  must  be  taken 
that  when  additions  of  acid  are  made  to  the  zinc  no  bubble  of 
air  is  introduced,  since  in  the  presence  of  air  the  arsenic  mirror 
may  become  black  and  unevenly  distributed,  instead  of  brown. 

Should  the  blank  experiment  not  be  satisfactory,  it  must  be 
ascertained  by  changing  the  materials  methodically  whether  the 
fault  lies  with  the  acid,  the  zinc,  or  the  apparatus. 

If  no  trace  of  a  mirror  is  obtained,  10  cc.  of  the  liquid  to  be 
tested  and  about  10  cc.  of  hydrochloric  acid  are  put  into  the 
funnel,  and  slowly  introduced  into  the  bottle  without  air-bubbles. 
Some  materials  (beers,  for  example)  are  apt  to  froth,  hence  the 
necessity  for  slow  introduction.  If  after  about  ten  minutes 
no  mirror  appears,  another  10  cc  of  the  liquid,  with  10  cc  of 
hydrochloric  acid,  are  added,  and  the  experiment  continued  foi 
fifteen  to  twenty  minutes,  acid  being  from  time  to  time  added  as 
may  appear  necessary. 

Preparation  of  Standard  Mirrors. — After  a  satisfactory  blank 
experiment,  a  series  of  standard  mirrors  may  be  prepared  under 
the  following  conditions: 

A  hydrochloric  acid  solution  of  arsenious  oxide,  containing  in 
each  cc  o-ooi  milligramme  AS2O3,  is  prepared  by  diluting  a 


ARSENIC   IN    I'OOD 


391 


stronger  solution  with  distilled  water.  Two  c.c.  of  this  solution 
(equal  to  0*002  milligramme  of  arsenious  oxide)  are  introduced 
into  the  apparatus,  a  new  tube  having  been  joined  to  the  drying- 
tube.  If  the  zinc  is  sensitive,  a  distinct  brown  mirror  is  obtained 
after  twenty  minutes.   It  is  important  to  note  that  some  "  pure  " 


zinc  is  not,  from  a  cause  at  present  unknown,  sufficiently  sensitive ; 
that  is  to  say,  the  addition  of  minute  quantities  of  arsenic  pro- 
duces no  mirror.  The  portion  of  the  tube  containing  the  mirror 
should  be  sealed  off  while  still  filled  with  hydrogen,  as  in  contact 
with  air  the  mirrors  gradually  fade.  Mirrors  are  now  similarly 
made  with  0*004,  o-oo6,  o-oo8  and  o-oi  milligramme  of  arsenious 


392  LABORATORY   WORK 

oxide.  With  a  little  practice  it  is  easy  to  obtain  the  deposits  of 
arsenic  neatly  and  equally  distributed.  The  standard  mirrors, 
properly  marked,  are  mounted  on  a  white  card  or  porcelain  slip. 
It  is  to  be  understood  that  the  first  stage  of  the  collection  of 
evers'  mirror  must  be  a  blank  of  at  least  twenty  minutes. 

As  an  additional  precaution  a  fresh  tube  should  always  be 
substituted  for  that  containing  the  mirror,  and  the  experiment 
continued  for  a  further  period  of  fifteen  minutes.  Should  a 
second  mirror  be  formed,  the  quantit}^  of  arsenic  to  which  it 
corresponds  is  added  to  that  shown  by  the  first. 

To  obtain  uniformly  brown  deposits  of  arsenic,  the  current  of 
hydrogen  should  be  slow,  combined  with  a  sparing  evolution 
of  arsenic  hvdride,  the  latter  condition  being  brought  about  by 
the  gradual  addition  of  the  arsenical  substance  to  the  Marsh 
apparatus.  The  rate  of  the  hydrogen  current  may  be  judged 
by  the  size  of  the  flame  at  the  open  end  of  the  tube  (W.  Ackroyd) . 
W.  Thomson  has  pointed  out  that  there  is  an  advantage  in 
cooling  the  portion  of  the  tube  arranged  for  receiving  the  mirror ; 
and  also  in  always  destroying  (by  oxidation)  the  organic  matter, 
when  this  is  markedlj^  present,  before  commencing  tests  for 
arsenic. 

It  must  be  recognized  that  the  tests  are  only  approximate, 
and  that  mirrors  corresponding  to  less  than  o"003  milligramme 
of  arsenious  oxide  cannot  be  safely  relied  upon.  When  a  mirror 
has  been  obtained,  a  duplicate  test  should  alwa^'s  be  made  in 
order  to  preclude  error  by  accidental  contamination. 

The  proof  that  a  mirror  is  arsenical  may  be  obtained  as  follows:  • 
The  narrow  portion  of  the  tube  containing  the  mirror  is  cut  off, 
the  hydrogen  replaced  by  air,  and  the  ends  sealed  up.  The 
tube,  held  in  the  tongs,  is  then  drawn  repeatcdl}'  through  the 
flame  of  a  Bunsen  lamp  until  the  mirror  has  disappeared.  On 
cooling,  minute  crystals  of  arsenious  oxide  deposit,  the  sparkling 
of  which  can  be  seen  with  the  naked  eye  if  the  tube  be  held  before 
a  luminous  flame,  and  they  can  be  readily  identified  under  the 
microscope  b}^  their  crystalline  forms. 

In  order  to  obtain  crystals  easily  examined  under  the  micro- 
scope, Delepine's  plan  is  to  cause  the  crystals  to  form  on  a  cover- 
glass.  For  this  purpose  he  uses  the  contrivance  shown  and 
described  in  Fig.  86. 

Gutzeit's  test  for  arsenic  is  as  follows:  To  a  small  flask  con- 
taining pure  Zn  and  dilute  HCl,  a  drop  of  PtCli  and  the  concen- 


ARSENIC   IN   WALL-PAPERS,    ETC.  393 

trated  liquid  (beer,  etc.)  are  added,  and  the  hydrogen  generated 
is  passed  through  a  dry  tube  containing  a  diy  strip  of  lead 
acetate  paper;  this  strip  of  paper  traps  the  sulphur  compounds 


FIG.  86. — s.  delepine's  apparatus  for  the  collection  on  a  cover- 
glass  OF  arsenious  acid  from  deposits  of  arsenic  on  copper. 

I,  Thick  iron  plate,  which  must  not  be  allowed  to  get  very  hot  during  the 
heating  of  3;  2,  cone  made  of  "  electric  "  copper  foil  absolutely  free 
from  arsenic;  3,  small  pieces  of  copper  covered  with  deposit  of  arsenic 
and  placed  in  the  portion  of  the  cone  which  must  be  brought  to  a 
dull-red  heat  by  means  of  the  flame  from  a  Bunsen  burner  (4) ;  5,  cover- 
glass. 

and  the  black  stain  may  be  seen  half-way  up  the  paper;  the 
arseniuretted  hydrogen  escapes,  and  if  a  strip  of  dry  HgClg  paper 
is  held  at  the  mouth  of  the  tube  a  yellow  stain  is  found  on  the 
paper.     This  reaction  is  exceedingly  dehcate. 


Trite  Examination  of  Wall-Papers,  Curtains,  Carpets, 
Linoleum,  Artificial  Flowers,  etc.,  for  Arsenic. 

The  dangers  which  may  arise  from  the  presence  of  this 
poisonous  agent  in  wall-papers,  etc.,  are  well  appreciated  and 
have  been  frequently  demonstrated.  There  is  a  widespread 
impression  among  the  general  public  that  green  is  the  only  colour 
likely  to  contain  this  dangerous  agent;  this  is  far  from  the  truth, 
though  the  metal  has  been  found  more  commonly  in  that  colour 
than  in  any  other. 

Almost  any  colour  may  be  arsenical;  and  it  may  be  accepted 
that  since  the  colour  green  is  so  generally  associated  with  arsenic 


394  LABORATORY  WORK 

in  tlic  popular  mind,  that  colour  is  the  most  likely  to  be  kept 
free  from  arsenic  by  manufacturers.  Indeed,  it  is  a  fact  that 
Scheele's  green  is  never  now  employed  for  colouring  wall-papers 
or  carpets  and  curtains. 

Arsenical  compounds  are  sometimes  also  used  as  mordants  to 
fix  the  dye  upon  materials. 

The  metal  is  commonly  dissociated  from  arsenical  wall-paper 
in  the  form  of  volatile  arsenical  compounds.  Small  grains  of 
arsenious  acid  sometimes  also  enter  the  atmosphere,  from  carpets, 
rugs  and  furs,  in  a  suspended  form,  and  (rarely)  even  metallic 
arsenic  may  thus  be  given  off;  so  that  a  microscopic  examina- 
tion of  the  dust  of  a  room  may  possibly  disclose  the  presence  of 
minute  octahedral  crystals  and  flakes. 

Long  ago  Gmelin  showed  that  of  rooms  with  arsenical  wall- 
paper, those  situated  on  ground-floors  or  in  other  positions 
favouring  dampness  were  most  dangerous  to  live  in.  Abel 
showed  that  this  was  due  to  the  action  of  moulds,  which  derived 
their  necessary  moisture  and  nourishment  from  the  paste  on 
the  wall-paper.  The  nature  of  the  arsenical  compound  given 
off  is  not  known,  but  it  possesses  the  garlic  smell  characteristic 
of  arseniuretted  hydrogen.  Aspergillus  glaiicus,  A.  niger  and  a 
form  of  Mncor  miiccdo  can  produce  this  change,  but  Penicillium 
hrevicaule  is  the  best  organism  for  the  following  test:  The  sus- 
pected article  reduced  to  a  state  of  fine  division  is  added  to 
moistened  breadcrumbs  contained  in  a  lOO  c.c.  flask.  After 
sterilization  the  contents  are  inoculated  with  the  mould,  the 
cotton  plug  of  the  flask  is  covered  by  a  caoutchouc  cap,  and  the 
whole  set  to  incubate  for  one  or  two  days  at  ^y°  C.  If  arsenic 
be  present,  the  garlic  odour  is  readily  detected  on  removing  the 
caoutchouc  cap.  The  method  is  even  \'aluable  when  the  arsenic 
is  present  in  very  small  quantity. 

If  Scheele's  green  is  suspected  of  furnishing  the  colour,  a  little 
of  the  paper  or  cloth  may  be  thoroughly  well  soaked  in  ammonia, 
when  a  blue  colour  is  created.  In  no  case,  however,  can  the 
employment  of  either  Reinsch's  or  Marsh's  test  be  dispensed 
with. 

In  applying  Marsh's  test,  the  paper,  carpet  or  cloth,  etc.,  is  cut 
up  into  small  pieces,  and  these  are  introduced  into  the  apparatus. 
Advantage  should  be  taken  of  the  pattern.  When,  for  instance, 
this  consists  of  flowers  and  leaves  of  different  colours,  these 
should  be  cut  out,  sorted  according  to  their  colours,  and  scrapings 


ARSENIC    IN   WALL-PAPERS,    ETC.  395 

or  extracts  of  each  colour  should  be  separately  intrfxluced  into 
the  flask  and  tested. 

T.  E.  Thorpe  recommends  the  following  procedure:  A  weighed 
portion  of  the  sample,  cut  into  pieces  of  convenient  size,  is 
placed  in  a  platinum  dish  of  about  7-5  centimetres  in  diameter, 
and  moistened  with  hot  water.  When  the  water  has  been 
absorbed  by  the  fabric,  20  c.c.  of  arsenic-free  lime-water  and 
0-5  gramme  of  calcined  magnesia  are  added,  the  latter  being 
stirred  with  a  glass  rod  among  the  pieces  of  the  fabric.  The 
platinum  dish  is  then  placed  on  a  hot  plate  or  over  a  small 
Bunsen  flame  and  the  liquid  evaporated.  The  dried  material  is 
then  thoroughly  charred  and  heated  in  a  muffle  furnace  until 
practically  all  the  carbon  is  burnt  off.  When  cold,  the  ash  is 
moistened  with  water  and  20  c.c.  of  dilute  sulphuric  acid 
added.  The  dish  is  warmed,  and  the  contents  transferred  to  a 
flask  of  about  120  c.c.  capacity.  Half  a  gramme  of  potassium 
metabisulphite  is  added,  and  the  solution  boiled  until  free  from 
sulphurous  acid.  The  liquid  is  cooled,  and  diluted  to  a  bulk  of 
50  c.c.  in  a  calibrated  flask  01  measuring  tube.  An  aliquot 
portion  may  then  be  taken  for  Marsh's  test. 

The  amounts  of  lime-water  and  magnesia  given  above  have 
been  proved  by  direct  experiment  to  retain  amounts  of  arsenic 
ranging  from  0-0025  to  5  milligrammes,  when  contained  in 
2  grammes  of  wool  or  paper. 

The  reduction  of  the  solution  with  sulphurous  acid  before 
addition  to  the  apparatus  is  necessary,  since,  under  the  conditions 
of  the  experiment,  arsenic  in  the  form  of  an  arsenate  or  arsenic 
acid  does  not  yield  arseniuretted  hydrogen. 

Arsenic  may  exist  in  varying  quantity  in  different  materials — 
■i.e.,  from  a  fraction  of  a  grain  (of  arsenious  acid)  to  many  grains 
per  square  yard;  but  since  very  small  amounts  will  condemn 
the  article  containing  it,  there  is  often  no  necessity  to  go  into 
the  matter  of  a  quantitative  analysis. 

The  presence  of  arsenic  in  aniline  dyes  is  rarety  exemplified 
by  the  appearance  of  a  rash  upon  the  skin  of  those  whose  under- 
clothing is  coloured  by  arsenical  dyes.  More  especiafly  is  this 
the  case  with  scarlet  and  blue  stockings;  and  the  legs  in  con- 
sequence are  the  commonest  seats  of  such  eruptions. 

In  order  to  test  the  extent  to  which  arsenical  colours  are  now 
employed,  Dr.  Dove  undertook  an  inquiry,  at  the  writer's 
suggestion,  in  1913. 


396  LABORATORY  WORK 

Of  the  forty-three  materials  examined,  thirty-four  (79-0  per 
cent.)  gave  negative  results,  two  (4-6  per  cent.)  gave  mirrors 
corresponding  to  the  presence  of  0-005  milligramme  of  arsenic 
{AS2O3)  in  the  gramme  of  material  (viz.,  5  parts  per  million), 
three  (6-9  per  cent.)  gave  about  half  that  quantit}',  and  four 
(9-3  per  cent.)  only  a  very  slight  trace.  Of  the  two  articles  which 
gave  0-005  milligramme  of  arsenic  one  was  orange  colour,  and 
the  other  yellow,  and  both  were  cloth  materials;  of  the  three 
which  showed  half  the  above  amount,  two  weie  dark  and  light 
olive  green  cloths,  and  one  a  sort  of  mulberry-coloured  silk; 
of  the  four  showing  only  a  very  slight  trace  of  arsenic,  one  was 
orange  silk,  and  three  were  heliotrope,  lavender,  and  emerald 
green  cotton  material.  The  cheap  socks,  which  were  green,  blue, 
and  violet  in  colour,  gave  negative  results. 

Eighteen  wall-papers  of  different  qualities,  colours,  and  prices 
were  next  examined.  When  different  colours  were  present,  or 
even  different  shades  of  the  same  colour,  each  colour  was 
separately  tested.  Ten  (55-5  per  cent.)  of  these  materials  gave 
negative  results,  two  (ii-i  per  cent.)  gave  about  0-0025  milli- 
gramme of  arsenic  (AS2O3),  and  six  (33-3  per  cent.)  furnished 
but  a  very  slight  trace.  The  two  which  gave  about  0-0025 
milligramme  of  arsenic  were  a  green  paper  with  mauve  flowers 
and  a  gamboge  yellow  paper  with  a  flower  pattern  in  a  lightei 
shade.  In  the  case  of  the  first  paper  mentioned  the  arsenic  was 
found  to  be  almost  wholly  in  the  mauve  flowers. 

Zinc,  chromium  and  tin  are  other  poisonous  me<-als  which  have 
been  found  in  coloured  textile  fabrics. 

The  presence  of  lead  in  carpets,  curtains,  etc.,  may  possibly 
induce  symptoms  of  chronic  lead-poisoning;  and  large  quantities 
are  commonly  contained  in  wall  paints  and  papers,  and  in  floor- 
cloths— chiefly  red  and  white.  An  examination,  therefore,  for 
the  presence  and  amount  of  this  metal  may  sometimes  become 
necessary. 

By  the  Regulations  of  the  Local  Government  Board,  191 2, 
made  under  the  Rag  Flock  Act,  191 1,  flock  manufactured  from 
rags  and  used  for  the  purpose  of  making  any  article  of  up- 
holstery, cushions,  or  bedding,  shall  be  deemed  to  conform  to 
the  required  standard  of  cleanliness,  when  the  amount  of  soluble 
chlorine  (in  the  form  of  chlorides)  removed  by  thorough  washing 
with  distilled  water,  at  a  temperature  not  exceeding  25°  C,  from 
not  less  than  40  grammes  of  a  well-mixed  sample  of  the  flock. 


ARSENIC   IN   WALL-PAPERS,    ETC.  397 

does  not  exceed  30  parts  of  chlorine  in  100,000  parts  of  the 
flock. 

Example. —  Forty  grammes  of  the  ilock  were  placed  in  a  large 
beaker,  distilled  water  was  added  until  a  laytr  floated  alove  the 
flock,  the  whole  was  then  covered  over  and  left  until  the  following 
day.  Clean  muslin  was  then  placed  over  a  large  filte  r-funnf  1, 
delivering  into  a  500  c.c.  flask,  and  the  soaked  flock  was  emptied 
on  to  the  muslin  and  well  squeezed.  It  was  next  opened  out, 
the  water  from  the  beaker  poured  on  to  it,  and  squeezed  out, 
and  finally  a  little  distilled  water  was  washed  through  the  flock, 
until  after  squeezing  it  500  c.c.  of  liquid  had  collected  in  the 
flask.  After  mixing  thoroughly  two  quantities  of  100  c.c,  each 
were  filtered  through  filter-paper.  In  one  portion  the  chlorine 
was  estimated  by  silver  nitrate  standard  solution  as  described 
in  water  analysis,  but  as  the  fluid  was  highly  coloured  and 
contained  sufficient  organic  matter  to  reduce  some  of  the  silver, 
the  result  was  only  taken  as  approximate. 

The  second  portion  of  100  c.c.  was  heated  on  the  water-bath 
with  plenty  of  strong  nitric  acid  (to  destroy  organic  matter), 
silver  nitrate  solution  was  then  added  in  excess  and  the  mixture 
heated,  until  the  chloride  of  silver  was  all  precipitated.  The 
precipitate  was  then  collected  on  a  weighed  filter-paper,  the 
filtrate  was  again  treated  with  nitrate  of  silver  and  refiltered, 
the  second  filtrate  being  quite  clear;  the  precipitate  was  then 
washed,  dried,  weighed,  and  calculated  to  chlorine  in  parts  per 
100,000. 

Supposing  that  the  100  c.c.  of  extract  contains  0-026  gramme 
AgCl.     Then  the  whole  500  c.c.  contains  0-13  gramme  AgCl. 

ButCl=^^^of  AgCl. 

143-34 
.*.  0*13  gramme  AgCl  =  0*03  gramme  CI. 

.•.  there  is  0*03  gramme  CI  in  40  grammes  of  flock,  or  75  parts 

per  100,000. 


PART    VI 

THE    EXAMINATION    OF   DISINFECTANTS 

In  judging  of  the  value  of  a  disinfectant  the  following  points 
should  demand  consideration: 

Its  germicidal  power,  in  presence  of  a  small  amount  of  organic 
matter;  as  to  whether  it  is  homogeneous  and  capable  of  remain- 
ing homogeneous  under  the  conditions  of  use;  at  the  strength 
in  which  it  is  employed  in  practice,  whether  it  is  poisonous  to 
higher  animals  (including  man),  affects  the  skin,  or  injures 
textile  articles  and  metal  surfaces;  whether  it  possesses  de- 
odorant properties;  and  its  relative  cost  compared  to  other 
disinfectants. 

Tar  preparations  contain:  (i)  Neutral  bodies;  light  and  heavy 
oils,  with  poor  disinfecting  properties.  (2)  Basic  bodies ;  aniline, 
pyridine,  etc.,  with  marked  disinfecting  properties.  (3)  Phenols; 
soluble  in  alkalies,  with  considerable  disinfecting  properties 
(especially  cresylic  acid  and  the  still  higher  homologues  of 
carbolic  acid) . 

The  phenols  are  obtained  from  the  distillates  of  coal  tar.  The 
fraction  distilling  from  tar  between  170°  to  230°  C.  is  called 
"  carbolic  oil,"  and  consists  chiefly  of  carbolic  acid  and  naph- 
thalene, but  it  also  contains  cresols  and  some  higher  homo- 
logues of  phenol.  The  phenols  are  extracted  from  the  mixture 
by  means  of  caustic  soda ;  the  separated  alkali  solution  is  decom- 
posed with  acid,  and  crude  carbolic  acid  separates  as  oil.  Crude 
carbolic  acid  contains,  besides  carbolic  acid,  cresols  and  higher 
phenols.  Pure  carbolic  acid  can  be  separated  by  distillation. 
Between  180°  to  182°  C.  carbolic  acid  distils  over;  the  tar  acids 
boiling  between  190°  to  200°  C.  are  chiefly  cresols,  and  the 
various  fractions  boiling  at  higher  temperatures  contain  other 
higher  homologues  of  phenol. 

399 


400  LABORATORY   WORK 

A  miscible  carbolic  disinfecting  fluid  may  consist  almost 
entirely  of  liquid  tar-oils  to  which  an  alkali  and  a  soap,  resin, 
or  gelatine  have  been  added  in  order  to  emulsify;  but  some 
contain  high  percentages  of  phenols. 

In  making  the  dilutions  of  coal-tar  disinfectants  with  hard 
water,  some  emulsions  partly  separate  out  almost  at  once; 
especially  is  this  so  in  the  higher  strengths  of  5  per  cent,  and 
over.  This  circumstance  is  explained  by  the  fact  that  in  coal- 
tar  disinfectants  the  oils  are  generally  either  combined  with  soap 
or  albuminous  material,  and  large  quantities  of  calcium  and  mag- 
nesium salts  in  water  may  cause  a  precipitation  of  the  soap  in  a 
soap  emulsion,  whereas  they  have  relatively  little  effect  upon 
an  albuminous  emulsion.  The  writer  and  M.  Wynter  Blyth 
have  pointed  out  the  close  relationship  which  exists  between  the 
germicidal  values  of  the  coal-tar  disinfectants  and  the  fineness  of 
the  emulsion,  and  that  it  is  not  possible  by  shaking  up  a  dis- 
infectant which  has  been  de-emulsified  by  admixture  with  hard 
waters  to  restore  the  emulsion,  or  any  but  a  small  proportion  of 
the  loss  of  germicidal  value. 

A  good  test  for  the  presence  of  phenol,  and  one  which  serves 
to  exclude  creosote,  consists  in  placing  a  few  drops  of  spirit  of 
nitrous  ether  in  a  test-tube,  and  then  adding  about  2  c.c.  of  a  very 
dilute  solution  of  the  phenol ;  if  sulphuric  acid  is  now  poured  down 
the  side  of  the  test-tube  a  purple  or  pink  colour  forms,  especially 
after  standing  awhile.  No  such  reaction  is  obtained  from  a 
dilute  solution  of  creosote  (Eykman). 

As  a  test  for  the  presence  of  carbolic  acid  or  phenol  in  a 
clear  and  colourless  solution,  ferric  chloride  solution  may  be 
added,  when  a  purple  colour  indicates  the  presence  of  phenol  or 
cresol.  A  better  test  for  phenol  is  the  addition  of  bromine 
water,  which  produces  a  white  precipitate  (tribromophenol) . 
Both  tests  are  rendered  more  delicate  when  applied  to  the  first 
portion  of  the  distillate  of  a  suspected  fluid. 

A  test  for  phenol  in  disinfecting  powders  may  be  performed 
by  adding  some  of  the  powder  to  water,  making  acid  with  sul- 
phuric acid,  distilling  over  and  adding  ferric  chloride  to  the 
distillate. 

Quantitatively,  carbolic  acid  is  estimated  by  the  process  of 
Koppeschaar.  The  phenol  is  precipitated  as  tribromophenol 
by  the  addition  of  excess  of  bromine  solution.  The  overplus 
of  bromine  is  determined  by  adding  potassium  iodide  from  which 


THE   EXAMINATION    OF    DISINFECTANTS  4OI 

the  bromine  displaces  iodine,  and  the  amount  of  tlic  latter  is 
found  by  titration  with  ^^  sodium  thiosul])hate  scjkition. 

CeHgOH  +  3Br2=  CeHaBrgOH  +  3HHr. 
Br2  +  2KI  =  2KBr  +  l2. 

2Na2S203  + 12  =  Na2S406  +  2NaI . 

.  The  bromine  solution  used  may  be  -^^j,  and  should  have  its 
strength  compared  with  the  NagSgOg.  (For  the  best  working 
details  of  the  process,  see  an  article  by  L.  V.  Redman,  A.  J. 
Weith  and  F.  P.  Brock,  published  in  the  Journal  of  Industrial 
and  Engineering  Chemistry,  No.  5,  p.  389,  1913.) 

The  following  procedure  (advocated  by  the  Lancet)  for  estima- 
ting the  tar  acids  in  disinfecting  fluids  is  simple  and  serviceable : 
Ten  grammes  of  the  disinfectant  are  made  up  to  100  c.c.  with 
water,  and  thoroughly  mixed;  100  c.c.  of  a  saturated  solution  of 
baryta,  to  which  a  few  crystals  of  barium  oxide  hydrate  are  added, 
are  brought  to  the  boil,  and  then  rapidly  filtered  into  a  flask  of 
about  300  c.c.  capacity.  The  diluted  disinfectant  is  slowly  added 
to  the  hot  baryta  water,  vigorously  shaking  the  mixture  all  the 
time.  This  results  in  the  separation  of  the  soaps  and  resins. 
It  is  now  filtered,  and  the  filtrate  made  up  to  300  c.c.  with  water, 
after  washing  the  residue  on  the  filter-paper.  Half  the  filtrate 
—i.e.,  150  c.c. — is  put  into  a  separating  flask,  made  acid  with 
HCl  (this  liberates  the  phenols),  and  then  50  c.c.  of  ether  added, 
and  the  whole  well  shaken.  On  standing,  the  ether,  which  has 
dissolved  the  phenols,  will  separate  out.  The  brown  solution 
below  should  be  tapped  off  into  another  separating  flask,  and 
the  ether  into  a  weighed  platinum  dish.  Another  50  c.c.  of 
ether  are  added  to  the  solution  tapped  off  into  the  second 
separating  flask,  and  the  extraction  repeated,  and  the  ether  is 
then  added  to  the  former  ether.  The  entire  ether  is  now  driven 
off,  the  dish  placed  in  a  hot-air  oven  for  ten  minutes  at  a  tem- 
perature of  50°  C,  and  then  reweighed.  The  weight  of  phenol- 
oids  so  obtained  multiplied  by  20  gives  the  percentage  of 
phenols  present  in  the  disinfectant.  The  phenoloids  are  now 
.dissolved  in  caustic  soda  solution,  and  then  made  up  to  the 
100  c.c.  with  water.  Take  5  c.c.  of  this,  dilute  with  water,  make 
strongly  acid  with  HCl,  and  run  in  a  ^  solution  of  bromine  in 
caustic  soda  until  a  permanent  yellow  colour  is  produced.  The 
number  of  cubic  centimetres  required,  multiplied  by  1-248,.  gives 
the  bromine  value,  in  terms  of  pure  carbolic  acid,  of  the  per- 

26 


402  LABORAtOKV    WORK 

centagt:  of  phenols  present.  If  this  result  agrees  with  the  per- 
centage of  phenols  by  weight,  the  phenoloids  are  pure  carbolic 
acid.  If  there  is  a  great  difference  between  the  two  results, 
carbolic  acid  may  be  considered  absent,  the  disinfecting  agent  in 
that  case  being  one  or  more  of  the  homologucs  of  carbolic  acid. 

For  the  determination  of  the  tar-oils  in  crude  carbolic  acid  the 
following  simple  method  giv^en  by  A.  H.  Allen  will  suffice:  Intro- 
duce 10  c.c.  of  the  sample  into  a  graduated  tube,  and  add  gradu- 
ally, noting  the  effect  produced,  four  times  its  volume  of  a 
ID  per  cent,  solution  of  caustic  soda,  free  from  alumina.  Then 
close  the  tube  and  agitate  well.  The  coal-tar  acids  will  be 
completely  dissolved  by  the  alkaline  liquid;  whilst,  on  standing, 
the  neutral  oils  will  form  a  separate  stratum  above  or  below  the 
other,  according  as  the  admixture  consisted  of  the  light  or  heavy 
"  oil  of  tar."  By  the  volume  occupied  by  the  oily  stratum  the 
extent  of  the  adulteration  is  at  once  indicated.  After  noticing 
whether  the  tar-oils  are  light  or  heavy,  a  volume  of  petroleum 
spirit,  equal  to  that  of  the  sample,  may  be  advantageously  added; 
its  employment  facilitates  the  separation  of  the  oily  stratum, 
and  renders  the  reading  of  its  volume  more  easy  and  accurate. 
Of  course,  the  volume  of  the  petroleum  spirit  used  must  be 
deducted  from  that  of  the  total  oily  layer. 

The  amount  of  water  present  with  phenol  may  be  found  by 
shaking  the  sample  in  a  graduated  cylinder  with  half  its  volume 
of  a  saturated  solution  of  sodium  chloride.  The  reduction  in  the 
volimie  of  the  phenol  indicates  the  amount  of  water  present.  If 
the  sample  is  pure,  it  contains  no  water,  but  crude  acids  may 
contain  15  per  cent,  or  over. 

The  specific  gravity  of  crude  carbolic  acid  should  be  between 
1-050  and  1-065,  9-iid  ^f  it  is  below  1-050  it  is  probably  adulterated 
with  light  tar-oil. 

In  some  cases  the  base  of  carbolic  powders  is  slaked  lime,  when 
the  carbolate  of  lime  formed  is  of  little  value  as  a  disinfectant. 
\Vhen  specif\'ing  for  the  supply  of  carbolic  powder,  a  percentage 
of  tar  acids  (generally  15  per  cent.)  should  be  demanded,  together 
with  the  guarantee  of  an  inert  base,  which  does  not  enter  into 
chemical  combination.  The  carbolic  acid  is  often  added  to 
silicious  matter  ("  carbolized  silicate  powders  ")  or  to  peat 
("  carbolized  peat  powders  "). 

The  percentage  of  phenols  and  crcsols  present  in  carbolic 
powders,  in  which  phenols  are  not  in  chemical  combination,  may 


THE   EXAMINATION   OF    DISINFECTANTS  403 

be  readily  arrived  at  by  the  following  means:  If  the  powdci 
contains  no  hme,  50  grammes  of  the  powder  are  thoroughly 
shaken  up  in  ether,  and  thus  all  the  free  and  available  tar  acids 
are  abstracted;  to  this  extract  is  added  50  c.c.  of  10  per  cent, 
caustic  potash  solution;  and  gentle  heat  is  applied  to  drive  off 
the  ether.  The  alkaline  liquid  having  been  boiled  down  and 
then  emptied  into  a  graduated  cylinder,  50  per  cent,  sulphuric 
acid  is  added  to  slight  acidity;  when  cold  the  tar  acids  separate 
out,  and  their  volume  can  be  read  off;  this  volume  x  2  will,  of 
course,  give  the  percentage  amount.  Then  the  percentage  of 
phenols  in  the  powder  is  to  the  amount  read  as  10-5  is  to  10,  for 
the  specific  gravity  of  phenol  is  about  1-050.  For  the  extraction 
of  the  total  carbolic  acid  in  powders  containing  lime,  in  which 
the  phenols  are  chemically  combined,  50  grammes  of  the  powder 
are  cautiously  and  slowly  treated  with  sufficient  50  per  cent, 
sulphuric  acid  in  a  mortar  until  a  minute  particle  of  the  powder 
moistened  with  water  gives  an  acid  reaction  when  placed  on 
litmus-paper.  Calcium  sulphate  is  thus  formed,  and  the  carbolic 
acid  is  set  free.  The  powder  may  then  be  exhausted  with  ether, 
and  the  ethereal  extract  may  be  filtered  into  a  flask  containing 
50  c.c.  of  10  per  cent,  caustic  potash  solution.  The  contents  of 
the  flask  are  then  well  shaken  up,  and  the  ether  driven  off.  The 
liquid  is  then  emptied  into  a  graduated  cylinder,  and  50  per  cent, 
sulphuric  acid  is  added  to  slight  acidity,  when  the  coal-tar 
acids  that  separate  out  completely  on  the  liquid  becoming  quite 
cold  X  2  will  approximately  represent  their  percentage  volume. 

The  crude  carbolic  acid  obtained  should  always  be  examined 
for  neutral  tar-oils,  and  the  test  described  on  p.  400  will  generally 
be  sufficient  for  all  practical  purposes. 

Good  carbolic  acid  powders  generally  contain  from  12  to  18  per 
cent,  of  crude  carbolic  acid,  but  they  are  liable  to  lose  i  or  2  per 
cent,  by  volatilization.  Half  of  the  total  oils  in  some  pow'ders 
consist  of  neutral  tar-oils  (Allen). 

Bleaching  Powder. — When  treated  with  HCl,  bleaching  powder 
gives  off  chlorine: 

Qa(0Cl)2  +  4HCI  =  2CI2  +  CaCl.2  +  2H2O ; 

and  the  liberated  chlorine  will,  by  liberating  iodine,  turn  a  white 
potassium  iodide  and  starch  paper  blue  (due  to  iodide  of  starch). 
To  confirm  the  presence  of  bleaching  powder,  calcium  should  also 
be  tested  for. 


404  LABORATORY   WORK 

To  estimate  the  available  chlorine  in  chloride  of  lime,  chlorinated 
soda,  etc.,  solutions  of  decinormal  iodine  (12-69  grammes  to  the 
litre)  and  of  arsenious  acid  (4-95  grammes  of  pure  arsenious  oxide 
and  20  grammes  of  sodium  bicarbonate  to  the  Htre)  are  employed. 

One  gramme  of  chloride  of  lime  is  rubbed  up  with  water  in 
a  mortar,  and  made  up  to  100  c.c.  Ten  c.c.  of  the  turbid  liquid 
(pre\-iously  well  shaken)  are  placed  in  a  white  porcelain  dish, 
which  thus  contains  o-i  gramme  of  the  chloride  of  Ume.  The 
arsenious  solution  is  added  to  slight  excess,  as  shown  by  the 
fact  that  iodide  of  potassium  and  starch  paper  is  no  longer  blued. 
Now  add  fresh  starch  solution,  and  run  in  the  iodine  solution  until 
a  faint  blue  tint  remains  permanent,  when  the  amount  of  the 
iodine  solution  required  corresponds  to  the  excess  of  arsenious 
solution  used.  Deduct  this  from  the  number  of  c.c.  of  the 
arsenious  solution  added  (for  the  two  decinormal  solutions  are 
chemically  equivalent),  and  the  difference  represents  the  amount 
of  arsenious  solution  which  is  oxidized  by  o-i  gramme  of  chloride 
of  lime.  Each  c.c.  of  the  arsenious  solution  =  0-00354  gramme 
of  available  chlorine. 

In  chloride  of  lime  solution  the  available  clilorine  is  that  exist- 
ing as  hypochlorite,  Ca(C10)2,  which  readily  breaks  up  into  CaClg 
and  O2,  and  the  starch  is  not  permanently  blued  until  all  the 
arsenious  acid  is  oxidized  to  arsenic  acid.  When  the  arsenious 
solution  is  added  it  combines  with  the  oxj'gen  to  form  arsenic 
acid;  but  when  present  in  excess  some  arsenious  acid  remains, 
and  this  is  measured  by  the  iodine. 

Several  estimations  should  be  made  and  the  mean  figure  taken, 
and  the  strength  of  the  iodine  solution  should  be  checked  against 
the  arsenious  acid  prior  to  use. 

Example. — Ten  c.c.  of  a  chlorine  disinfectant  solution  taken. 
Sixty  c.c.  of  y^  arsenious  solution  were  added.  Added  y^  iodine 
until  blue  tint  remained;  3  c.c.  were  required.  Therefore, 
available  chlorine  in  the  10  c.c.  of  sample ^60— 3  =  57  c.c. 
Y*^  iodine  =  57  c.c.  xo"  arsenious  solution.  But  i  c.c.  of 
y~  arsenious  solution  =0-00354  gramme  of  chlorine. 

.-.  57  c.c.  =  0-2  gramme  of  chlorine  in  10  c.c.  of  sample. 
=  2  grammes  of  chlorine  in  100  c.c.  of  sample. 

.-.  There  is  approximately  2  per  cent,  of  available  clilorine 
present. 

Formalin  may  be  detected  by  distilling  some  of  the  liquid 
into  a  test-tube,  adding  to  the  distillate  a  drop  of  5  per  cent. 


THE    EXAMINATION    OF    DISINFECTANTS  4O5 

carbolic  acid,  and  running  down  tlic  side  of  the  tube  strong 
sulphuric  acid,  when  a  crimson  zone  results  if  formalin  is  present. 

A  solution  of  the  perchloride  of  mercury  furnishes  a  yellow 
precipitate,  soluble  in  excess,  with  potassium  iodide. 

Copper  sulphate,  zinc  chloride,  and  ferrous  sulphate  in  solution 
may  be  tested  by  methods  previously  indicated  in  dealing  with 
water  analysis. 

A  sulphurous  acid  solution  will  furnish  a  white  precipitate 
with  silver  nitrate,  which  is  soluble  in  nitric  acid;  or  if  some 
granulated  zinc  and  hydrochloric  acid  are  added  to  the  solution, 
and  a  piece  of  moistened  lead  paper  is  held  over  the  mouth  of  the 
flask  containing  it,  the  paper  will  be  darkened  from  the  pro- 
duction of  sulphuretted  hydrogen. 

The  sulphurous  acid  contained,  along  with  other  disinfectants, 
in  some  disinfecting  powders,  may  be  estimated  by  shaking  up 
I  gramme  of  the  finely  crushed  powder  in  a  large  quantity  of 
freshly  distilled  water,  so  as  to  make  the  solution  very  dilute; 
50  c.c.  of  decinormal  iodine  are  run  in;  the  mixture  is  then  made 
distinctly  acid  with  dilute  hydrochloric  acid,  and  the  excess  of 
iodine  is  titrated  with  decinormal  thiosulphate.  Each  c.c.  of  the 
iodine  solution  reduced  by  the  powder=  0-0032  gramme  of  502- 

To  test  the  strength  of  a  solution  of  permanganate  a  known 
volume  of  a  decinormal  solution  of  oxalic  acid  (6-3  grammes  per 
litre)  is  placed  in  a  beaker,  and  dilute  sulphuric  acid  is  added  until 
the  solution  is  strongly  acid ;  the  diluted  permanganate  solution  is 
then  run  in  from  a  burette  until  a  permanent  pink  colour  remains. 

5H2C2O4  +  KaMuaOg  +  3H2SO4  =  K2SO4  +  2MnS04  + 1  oCOg  +  8H2O ; 
and  therefore  5  equivalents  of  oxalic  acid  require  for  oxidation 
I  equivalent  of  permanganate  (containing  5  atoms  of  available 
oxygen). 

Therefore,  to  determine  the  presence  of  permanganate  it  is  only 
necessary  to  acidify  with  dilute  sulphuric  acid,  add  oxalic  acid 
and  warm,  when  the  pink  colour  disappears. 

The  disinfecting  power  of  a  disinfectant  can  only  be  gauged 
by  direct  experiments  upon  micro-organisms. 

The  Determination  of  Antiseptic  and  Germicidal 
Power. 

The  three  factors — strength  of  the  solution,  duration  of  action, 
and  nature  of  the  material  acted  upon — cannot  be  disassociated. 
If,  for  instance,  we  ascertain  that  a  given  strength  of  mercuric 


4")6  LABORATORY    WORK 

chloride  will  kill  typhoid  bacilli  in  broth  culture  in  half  an  hour, 
we  should  still  be  ignorant  of  the  strength  which  would  be 
sufficient  in  the  same  time  to  render  typhoid  f?eces  harmless  as 
a  factor  in  the  spread  of  enteric  fever. 

It  is  very  difficult  to  define  standard  conditions  for  testing 
purposes,  because  in  practice  disinfectants  are  employed  as 
germicides  under  a  variety  of  conditions. 

Madsen  and  Nyman,  and  also  H.  Chick,  have  shown  that 
when  the  disinfectant  is  present  in  considerable  excess,  the 
process  of  disinfection  proceeds  in  accordance  with  a  definite  law, 
the  number  of  living  bacteria  per  unit  volume  progressively  and 
regularly  decreasing  with  increase  of  time,  in  a  logarithmic  ratio. 

Investigations  may  be  required  to — 

1.  Determine  the  restraining  and  germicidal  power  of  different 
substances  in  solution. 

2.  Determine  the  germicidal  power  of  substances  when 
volatilized. 

To  Determine  Lethal  Pcncer. — Two  separate  determinations 
may  have  to  be  made,  one  for  the  bacterium  and  one  for  the 
spore,  if  spores  are  produced. 

In  ascertaining  lethal  power  it  is  very  important  to  be  certain 
that  none  of  the  germicide  is  carried  over  into  the  cultivation  solu- 
tion, as  a  very  small  amount  may  be  sufficient  to  inhibit  growth. 
In  practice  it  is  extremely  difficult  to  get  rid  of  all  traces  of 
antiseptic. 

The  "  garnet  method  "  of  Kronig  and  Paul  (1897)  is  a  valuable 
one,  but  on  the  whole  the  "  drop  method  "  is  the  most  con- 
venient method  for  determining  the  germicidal  action  of  any 
given  substance  for  the  ordinary  bacteria. 

In  the  garnet  method  garnets  of  similar  size  are  selected,  and 
after  careful  cleaning  are  dipped  into  a  filtered  watery  emulsion 
of  sporing  anthrax  or  other  bacillus  selected.  The  emulsion 
is  allowed  to  dry  on  them  in  a  thin  film.  The  loaded  garnets 
are  then  immersed  in  the  disinfectant  solutions  under  investi- 
gation. After  definite  periods  of  time  the  garnets  are  taken  out, 
the  disinfectant  carried  over  removed  by  gentle  washing,  and  (if 
necessary)  washed  in  agents  (such  as  ammonium  sulphide,  if 
mercuric  chloride  is  used)  to  render  inert  any  trace  of  disinfectant. 
The  bacteria  or  spores  are  then  separated  from  the  garnets  by 
shaking  them  in  water.  Definite  amounts  of  the  washings  are 
tlien  cultivated  and  the  bacteria  counted. 


DETERMINATION    OF   ANTISEPTIC    POWKK 


407 


It  is  convenient  to  compare  the  germicidal  power  with  thai  of 
some  standard  disinfectant  under  carefully  standardized  con- 
ditions. Rideal  and  Walker's  method  is  the  best  yet  devised 
for  this  purpose. 

In  the  Ri deal-Walker  method  a  carefully  standardized  pure 
carbolic  acid  solution  is  used  as  a  control,  accurate  dilutions  in 
sterile  distilled  water  being  prepared.  A  twenty-four  hours' 
broth  culture  (Lemco),  grown  at  37°  C,  of  B.  typhosus  is  the  test 
organism,  and  a  reaction  of  +1-5  for  100  c.c.  broth  is  recom- 
mended. The  temperature  of  the  room  should  be  from  15°  to 
18°  C.  during  the  experiment. 

To  5  c.c.  of  a  particular  dilution  of  the  disinfectant  in  sterilized 
water  0-2  c.c.  of  the  broth  culture  is  added,  and  the  mixture 
well  shaken.  Then  subcultures  are  taken  every  two  and  a  half 
minutes  up  to  fifteen  minutes.  The  subcultures  are  made  in 
broth  and  incubated  for  at  least  forty-eight  hours  at  37°  C. 
Those  with  a  growth  are  then  entered  in  the  tables. 

A  number  of  different  dilutions  of  the  disinfectant  under 
examination,  and  also  one  or  more  dilutions  of  the  carbolic  acid, 
are  tested  at  the  same  time,  and  under  precisely  similar  con- 
ditions of  temperature,  amount  of  disinfectant  solution  used, 
quantity  of  typhoid  broth  culture  added,  etc.  The  efficiency 
of  the  disinfectant  is  expressed  in  multiples  of  carbolic  acid  per- 
forming the  same  work — i.e.,  a  dilution  of  the  disinfectant  which 
does  the  same  work  as  the  standard  carbolic  acid  dilution  is 
obtained ;  the  ratio  obtained  by  dividing  the  former  by  the  latter  is 
called  the  "  carbolic  acid  coefficient."  The  results  are  conveni- 
ently recorded  in  tables,  of  which  the  following  is  an  illustration : 

B.  Typhosus  Twenty-Four  Hours'  Broth  Culture  at  37°  C.     ' 
Room  Temperature  15°  to  18°  C. 


Sample. 

Dilution. 

Time  Culture  exposed  to  Action 
of  Disinfectant  in  Minutes. 

Subculture. 

25 

5 

7l 

10 

I2J 

15 

Period  of 
Incubation. 

Tempera- 
ture. 

Disinfectant  w. 
Disinfectant  w. 
Disinfectant  w. 
Carbolic  acid 

I  :  700 
1 :  800 
1 :  900 
1 :  90 

X 
X 
X 
X 

X 
X 
X 
X 

X 

X         X 

X 

Hours. 

-      48 

Centigrade. 

37° 

Carbolic  acid  coefficient  =  Vu"  =  7"  7- 


4o8 


LABORATORY   WORK 


A  test-tube  rack  with  holo;^  for  thirty  test-tubes  in  two  rows; 
small  flasks  and  covered  vessels  (Fig.  Sy) ;  a  dropping  pipette 
standardized  to  deliver  o-i  c.c.  of  broth  culture  per  drop;  an 
inoculating  needle  with  a  platinum  wire  providing  a  loop 
3  millimetres  internal  diameter  at  its  end,  are  required. 

0'5  c.c.  of  the  culture  is  placed  in  the  five  small  tubes,  and 
then  5  c.c.  of  the  five  different  dilutions  of  the  disinfectant  are 
also  added  to  the  tubes,  at  inter\'als  of  half  a  minute.  When  the 
fifth  tube  has  been  dealt  with,  the  organisms  in  the  first  tube 


Fig.  87. — Apparatus  employed  in  the  Rideal- Walker  Method. 

A ,  Test-tubes  containing  the  nutrient  medium  to  be  inoculated .  B,  Flasks 
containing  the  difierent  dilutions  of  phenol  and  the  disinfectant  under 
test.  C,  Small  covered  vessels  containing  02  c.c.  of  typhoid  culture, 
and  5  c.c.  of  particular  dilutions  of  the  disinfectant. 


will  have  been  exposed  to  the  disinfectant  for  two  minutes,  so 
after  waiting  another  half-minute,  a  loopful  of  the  mixture  in 
the  first  tube  is  inoculated  into  the  first  broth  tube;  and  so  at 
intervals  of  every  thirty  seconds  loopfuls  from  the  other  four 
tubes  are  in  turn  inoculated  into  their  properly  labelled  broth 
tubes.  When  the  fifth  broth  tube  is  inoculated,  the  organisms 
in  the  first  tube  v^^ill  have  been  exposed  to  the  disinfectant  for 
four  and  a  half  minutes,  so  the  operator  waits  half  a  minute 
before  again  inoculating  broth  tube  No.  i ;  and  so  in  seventeen 
minutes  inoculations  are  obtained  containing  organisms  which 
have  been  exposed  to  five  different  strengths  of  the  disinfectants 
for  six  two  and  a  half  minute  periods. 


DETERMINATION    OF    ANTISEPTIC    POWER  4OQ 

This  method  can  be  used  to  obtain  the  carl)o]ic  acid  coefficients 
for  other  organisms — for  example,  B.  peslis,  Sp.  oholercBci. 

Notes  on  the  Method. — Use  as  stock  organism  B.  typhosus  from 
an  agar  slope  culture  that  has  been  grown  at  21''  to  22"^  C. 
(70°  to  72°  F.)  from  two  to  five  days,  and  removed  by  weekly 
transference  for  several  uninterrupted  generations  from  the 
original  source  (the  human  body).  Carbolic  acid  is  frequently 
contaminated  with  cresol,  and  cresol  has  approximately  three 
times  the  bactericidal  efficiency  of  phenol.  In  order,  tnerefore,  to 
secure  uniform  conditions  of  testing,  it  is  necessary  to  work  with 
carbolic  acid  of  such  purity  that  the  sohdifying  point  exceeds 
40°  with  the  thermometer  in  at  least  50  c.c.  of  the  liquid.  A 
5  per  cent,  by  weight  stock  solution  is  then  prepared,  and 
standardized  by  titration  with  decinormal  bromine.  This  keeps 
well,  and  is  employed  for  making  the  necessary  weaker  dilutions 
for  test  purposes. 

The  composition  of  the  broth  employed  is — ■ 

20  grammes  of  Lemco. 
20  grammes  of  Witte's  peptone. 
10  grammes  of  sodium  chloride. 
I  litre  of  distilled  water. 

This  mixture  is  boiled  for  thirty  minutes,  filtered,  and  then 
neutralized  with  normal  NaHO,  using  phenolphthalein  as 
indicator.  The  broth  is  then  made  up  to  a  litre,  15  c.c.  of  normal 
HCl  is  added,  and  the  whole  sterilized.  The  exact  reaction  of  the 
broth  in  which  the  test  organism  is  grown  for  the  twenty-four 
hours  prior  to  the  test  is  a  matter  of  considerable  importance 
as  affecting  the  coefficient  obtained.  The  writer  has  known 
a  faultily  made  broth  to  reduce  coefficients  by  some  10  per 
cent. 

The  method  has  been  subjected  to  considerable  criticism,  but 
it  is  much  employed  for  standardizing  disinfectants  for  manu- 
facturers' purposes,  and  in  the  specifications  of  tenders  for 
supplying  disinfectants  it  is  often  required  that  disinfectants 
quoted  should  possess  a  certain  carbolic  acid  coefficient  as  deter- 
mined by  the  Rideal-Walker  process. 

To  obtain  identical  results  a  number  of  variants  have  to  be 
controlled,   even  such  apparently  trivial  matters  as  the  com- 


4IO  LABORATORY   WORK 

position  of  tlio  broth,  its  a£3;e,  the  particular  strain  of  bacillus, 
and  the  variation  in  temperature  of  medication,  exercise  consider- 
able influence  upon  the  results. 

In  particular  the  method,  and  all  similar  methods,  must  not  be 
taken  as  furnishing  without  much  modification  a  guide  to  the 
practical  use  of  disinfectants. 

The  practical  utility  of  any  disinfectant  depends  mainly  upon 
how  much  it  is  influenced  by  the  presence  of  organic  matter. 
The  efficiency  of  some  disinfectants  is  greatly  impaired  by  the 
presence  of  organic  matter,  while  for  others  a  less  diminution  of 
power  is  so  caused.  For  example,  Martin  and  Chick*  showed 
that  when  a  3  per  cent,  suspension  of  dried  finely-divided  faeces 
is  used,  the  efficiency  of  phenol  is  reduced  by  about  10  per  cent., 
while  that  of  the  emulsified  tar  acids  is  reduced  from  one-third 
to  one-eleventh  of  the  primary  value.  The  soluble  commercial 
cresols  occupy  an  intermediate  position,  the  reduction  depend- 
ing upon  the  solubility.  The  reduction  in  the  case  of  the 
emulsified  tar  acids  is  found  to  be  higher  the  finer  the  emulsion 
Some  disinfectants  are  more  efficient  against  one  species  of 
bacteria,  others  against  another.  In  the  case  of  spores  metallic 
salts  are  most  efficient.  The  removal  of  an  emulsion  of  higher 
phenols  by  bacteria  is  in  the  first  instance  a  process  of  adsorp- 
tion; disinfectants  which  form  fine  emulsions  possess  superior 
efficiency,  because,  owing  to  this  adsorption,  the  bacteria  rapidly 
become  surrounded  by  the  disinfectant  in  much  greater  con- 
centration than  exists  throughout  the  liquid. 

As  the  Rideal-Walker  method  does  not  take  into  account  the 
influence  of  the  presence  of  organic  matter,  various  attempts 
have  been  made  to  obviate  this  difficulty.  For  this  purpose 
the  addition  of  gelatine,  serum,  urine,  milk,  fteces,  etc.,  has 
been  suggested  by  different  workers,  so  that  the  germicidal 
power  of  the  disinfectant  may  be  tested  in  the  presence  of 
organic  matter.  None  of  these  additions  are  altogether  satis- 
factory, and  it  cannot  be  said  that  a  suitable  method  has  yet  been 
evolved.  The  effect  of  the  addition  of  these  organic  substances 
is  in  every  case  to  considerably  lower  the  coefficient  obtained 
with  what  may  be  styled  the  naked  germs;  but  the  coefficient 
of  some  disinfectants  (for  example,  potassium  permanganate) 
is  lowered  to  a  much  greater  degree  than  others. 

*  Journal  of  Hygiene,  1908,  vol.  viii.,  p.  654. 


DETERMINATION    OE   ANTISEPTIC   POWER  4II 

The  action  of  antiseptics  upon  certain  special  f)rg;i,nisms  f:annot 
be  tested  by  the  above  method.  As  a  good  illustration  of  this 
the  determination  of  the  germicidal  action  upon  tubercle  bacilli 
may  be  mentioned.  The  fresh  sputum  may  be  spread  upon  slips 
of  wood  or  other  substance,  and  dried  in  a  desiccator  over  sul- 
phuric acid.  Only  completely  dried  slips  should  be  used.  The 
slips  are  soaked  in  different  strengths  of  the  germicidal  solution 
under  examination  for  a  definite  time  {e.g.,  three  hours).  The 
slips  are  then  washed  in  sterile  water,  and  the  dried  expectora- 
tion scraped  off,  made  into  an  emulsion  with  sterile  water,  and 
injected  into  a  series  of  guinea-pigs.  If  tuberculosis  develops  it 
is  obvious  that  all  the  tubercle  bacilli  were  not  killed.  By  using 
an  appropriate  series  of  dilutions  the  correct  lethal  strength  for 
the  tubercle  bacillus,  under  the  conditions  of  the  experiment,  can 
be  ascertained. 

If  the  test  organism  produces  spores,  it  must  be  incubated 
first  under  optimum  conditions  for  spore  formation,  and  cultures 
used  which  contain  large  numbers  of  spores. 

To  Test  the  Action  of  Volatile  Disinfectants.- — Broth  cultures 
of  different  organisms  may  be  used.  B.  typhosus,  B.  diphtherics, 
and  B.  anihracis  are  convenient  to  employ. 

Sterile  strips  of  linen  or  wood  may  be  soaked  in  these  solutions, 
then  removed  and  dried  at  37°  C.  in  a  vacuum  over  sulphuric 
acid.  Such  inoculated  strips  are  exposed  to  the  action  of  the 
gaseous  disinfectant,  present  in  known  percentage,  for  definite 
but  varying  periods. 

Some  of  the  strips  should  be  exposed  freely  to  the  disinfectant, 
others  should  be  placed  in  the  centre  of  rolled  blankets,  etc. 

After  the  required  time,  the  strips  are  inoculated  into 
sterile  broth  tubes,  which  are  incubated  and  examined  for 
growth. 

The  dried  strips  are  conveniently  carried  in  sterile  Petri- 
dishes. 

All  the  different  factors  of  time,  percentage  of  disinfectant, 
temperature,  and  humidity  of  atmosphere,  should  be  carefully 
noted. 

In  the  case  of  most  volatile  disinfectants  a  sufhciency  of  mois- 
ture must  be  present  in  the  air  of  the  room  if  the  gas  is  to  exert 
its  disinfecting  properties  under  the  most  favourable  conditions. 
Thus,  sulphurous  acid  gas  generated  into  an  atmosphere  saturated 


412  LABORATORY   WORK 

with  moisture  has  almost  double  the  disinfecting  power  of  the 
gas  generated  in  a  dry  atmosphere;  and  formic  aldehyde  vapour, 
being  most  efficacious  at  a  temperature  of  70°  F.  and  a  relative 
humidity  of  70  per  cent.,  is  incapable  of  producing  its  best  results 
if  the  temperature  and  humidity  of  the  air  of  the  room  are  mucli 
below  these  optimum  conditions. 


INDEX 


Acarus  domesticus  (cheese  mite),  265; 
A.  farincs  (wheat  mite),  267;  A. 
sacchari,  339 

Acidimetry,  136-138 

Actinomycosis,  303-304 

Adam.'s  process  for  fat  extraction, 
236-237 

Adeney's  process,  150-152 

Agrostemma  githago  (corn  cockle), 
277-279 

Air,  composition  of,  173-174;  ex- 
amination of,  174-220;  carbonic 
acid,  1 79-191;  carbonic  oxide, 
196-202 ;  compounds  of  sulphur  in, 
202-204;  compounds  of  chlorine 
in,  204 ;  compounds  of  nitrogen  in, 
204,  205;  organic  matter,  192-194; 
phosphuretted  hydrogen,  204-205; 
arseniuretted  hydrogen,  204,  205; 
chlorine  and  bromine,  204,  205; 
eudiometric  determination  of  oxy- 
gen, 174-178;  collection  of  sam- 
ples, 180-181;  ammonia,  195; 
marsh  gas,  195-196;  amounts  of 
gaseous  impurities  injurious  to 
health,  205;  ozone,  206-209;  ozo- 
nometry,  209;  peroxide  of  hydro- 
gen, 209;  suspended  matter,  210- 
215;  marsh  air,  216;  sewer  air, 
216-217;  air  of  coal-mines,  217- 
218;  town  air  during  fogs,  218; 
ground  air,  218-219;  scheme  for 
detecting  large  quantities  of  gases, 
221-223;  bacteriological  note,  220 

Aitken's  method  of  counting  sus- 
pended particles  in  air,  213 

Alcohol,  estimation  of,  318-319; 
table,  320-321 

Alcoholic  beverages,  318-331;  proof 
spirit,  319;  spirits,  319-325;  wine, 
325-329;  beer,  329-331 

Algae  in  water,  28,  70 

Alkalimetry,  136-138 

Alum  in  bread,  280-283;  in  baking- 
powders,  278 

4 


Aluminium  for  canning  foods,  363 

Amanita  phalloides,  312 

Ammonia  in  water  {vide  Wanklyn's 

process);  in  air,  195 
Ammonium  sulphide  in  water,    104; 

in  air,  203,  222 
AnabcBna,  in  water,  26,  27,  28 
Anguillul(B  in  water,  66,  72 
Aniline  colours,  382-385 
Animalculae  in  water,  71-72 
Ankylostomum  duodenale,  72-73 
Annatto,  244,  383-384 
Antiseptic     and     germicidal     power, 

determination  of,  405-412 
Antiseptics  employed  in  provisions, 

364-382 
Arata's  wool  test,  385 
Arrowroot,  284,  288 
Arsenic  in  water,  46,  49;  in  air,  215; 

in  beer,  329-330;  in  food,  387-393; 

in  wall-papers,  393-396 
Arseniuretted  hydrogen  in  air,   204- 

205 
Ascaris  lumbricoides,  72,  74 
Aspergillus  glaucus,  70,  264,  270,  394 
Atomic  weights,  16 
Available  chlorine  in  chloride  of  lime, 

404 

Bacillus  acidus  lacticus,  226 

B.  botulinus,  306-308,  315 

B.  cadaveris  sporogenes,  359 

B.  coli  communis,  in  water,  1 26-1 28, 
130-131;  in  soil,  168-171;  in  air, 
220;  in  milk,  250-252;  in  shell-lish, 

311 

B.  enteritidis  sporogenes  in  water, 
126-128;  in  soil,  168-171;  in  air, 
220;  in  milk,  249-252;  in  food- 
poisoning,  306-311 

Bacillus  of  Gaertner,  306-311,  314 

B.  paratyphosus,  306 

B.  tuberculosis  in  milk,  249-252;  in, 
butter,  262 

Baking-powders,  278 

13 


414 


LABORATUKY    WORK 


Balances,  3 

Barium  in  water,  40 

Barley-meal,  2S5,  2Sj,  290 

Bean-meal,  2S4,  288 

Beet,  measly,  299 

Beer,  329-331 

Beggiatoa  alba,  29,  57,  69,  103,  154 

Benzoic  acid,  244,  379-380 

Bilharzia  hcBtnatobia,  73-74 

Bleaching  of  flour,  276 

Bleaching  powder,  403-404 

Boiled  milk,  247-248 

Boric  acid,  244,  327,  364-368,  373-375 

Bothriocephalus  latus,  299 

Botulismtis,  307-308,  314-315 

Brandy,  319";  321-322 

Bread,  278-283;  composition  of,  278; 

analysis,  279-280;  adulteration  of, 

280-283 
Bntchus  pisi,  288 

Brucine  test  (nitrates  in  water),  94 
Bunt,  269 

Burettes,  graduatcil,  15 
Butter,  composition  of,  253;  analysis 

of,  253-262;  adulteration,  254-262 

Caffein,  343,  345 

Calandra  granaria,  266 

Calcium  salts  in  water,  54-55 

Canned  food,  358-365 

Carbolic  acid,  399-403;  powders,  402 

Carbon  bisulphide  in  air,  204 

Carbonic  acid  in  water,  29,  30,  loi- 
102;  in  mineral  waters,  139-140; 
in  air,  179-191 

Carbonic  oxide  in  air,  196-202 

Camelly-^Iackie  process,  194 

Cayenne  pepper,  338 

Cellular  elements  in  milk,  240-241 

Cereals,  composition  of,  284-285 

Cheese,  262-265;  adulteration  of, 
263-264;  parasites  in,  264-265 

Chemical  antiseptics  in  food,  364-3SJ 

Chemical  balances,  3 

Chicory,  343-346,  347 

Chlorine  in  water,  31-36;  in  sea- 
water,  131-132;  in  air,  204-205, 
223;  as  disinfectant,  404 

Chocolate,  349 

Chromium  in  water,  46,  50 

Cladothrix  in  water,  69,  70 

Clark's  scale  of  hardness,  41 

Claviceps  purpurea,  267-269 

Clay  soil,  161-162,  171 

Cloves,  338 

Coal-gas  in  water,  28;  in  air,  197 

Coal-mines,  air  of,  217-218 

Coal-tar  dyes,  244 

Coccidia  oviformes,  297 

Cocoa,  347-349  I 


Cocoauut  od,  201 

Casnunis  ccrcbralis,  297 

Cortee,  343-347 

Collection   of   samples   of   water   for 

chemical' examination,    19-21;   for 

bacteriological    examination,    124- 

146;  of  soil,   158,  169;  of  air,  iSo- 

iSi ;  of  milk,  251 
Colostrum,  229,  240 
Colouring   agents   in    milk,    385;    in 

butter,  202;  in  wine,  328;  in  sugar, 

339;  in  food,  3S^-3^'^5 
Composition  of  water  from  various 

sources,  110-113 
Condensed  milk,  245-247 
Copper  in  water,  45,  47-4S,  51,  52;  in 

tinned  provisions,  363-364 
Copper-zinc    process    for    estimating 

nitrates  and  nitrites  in  water,  97-98 
Corn,  2O6-270;  parasites  in,  266-270 
Corn-cockle,  the,  277,  279 
Cornflour,  284 
Cotton-seed  oil,  261 
Cream,  225,  232,  243,  244-245 
Crenothrix  in  water,  2b,  29,  69 
Cresols  in  carbolic  powders,  402,  403 
Cryptomonas  in  water,  28 
Cysticercus     cellulosce,     298-299;     C. 

bovis,  299;   C.  pisiformis,  297;   C. 

tenuicollis,  297;  C.  serialis,  297 

Darnel  grass,  277 

Decinormal  solutions,  136-137 

Degrees  of  hardness  (Clark),  41 

Delepine's  apparatus  for  oxidation  of 
arsenic,  392;  apparatus  for  milk- 
collecting,  251 

Departmental  Committee  on  antisep- 
tics in  food,  371 

Deposited  matter  in  water,  64-74 

Desiccator,  the,  3 

Diphenylamine  test  for  nitrates,  94 

Dirt  in  food,  385-386 

Disinfectants,  399-412 

Dissolved  oxygen  in  water  (Thresh's 
process),  104-108;  Winkler's  pro- 
cess, 108-109;  in  sewage  effluents 
(Adeney's  process),  150-152;  Wink- 
ler method  (modified),  152-154 

Distoma  hepaticum,  304 

Dumas'  process  for  estimating  oxy- 
gen in  air,  17S 

Dupre's  estimation  of  alum,  2S2-2S3 

Dust  brand  in  wheat,  269 

Ear-cockle  in  wheat,  267 
Earth-nut  oil,  261 
Effluents,  sewage,  143-154 
Eggs,  2,^5 
Enriched  milk,  236 


INDEX 


415 


Enlev'o)Horpha  in  sea-water,  154 
J'.rgot,  2G7-2O9 
Eudiometer,  174-178 
Eudiometric  examination  of  air,  174- 
178 

Facing  tea-leaves,  354-355 

Fat  extraction,  9-10;  in  milk,   234- 

238;  in  butter,  254-260 
Fehling's  method,  340-341 
Filaria  in  water,  74 
Fish,  295,  299,  307,  310 
Fish  life  in  water,  123 
Flour,  wheat,  270-277 
Fluorides  as  antiseptics,  244,  3S1 
Fog,  air  duiing,  218 
Food  poisoning,  305-312 
Formalin,    244,    366,    369,    375-378, 

404-405 
Fraenkel's  borer,  170 
Frankland's  process  of  water  analysis, 

90-91 
Frozen  meat,  304-305 
Fungi,  edible,  312 
Furfural,  322-323 
Fusel  oil,  323-324 

Gas  burette,  Hempel's,  175-177 
Gaseous  impurities  in  air,  injurious 

amounts  of,  205 
Gases  in  water,  1 01- 109 
Gelatine  in  cream,  244 
Gerber's  method  for  fat  in  milk,  237- 

238 
Gin,  300 
Ginger,  338 
Glucose,  342 
Gluten,  272-274 
Graduated  burettes,  15 
Graveyards,  soil  of,  166 
Ground-air,  218-219 
Ground-water,  collection  of,  158 
Gutzeit's  test  for  arsenic,  392-393 

Haldane's  test  for  CO  in  air,  201-202; 
estimation  of  CO2  in  air,  187-190 

Halphen's  test  for  cotton-seed  oil,  261 

Hardness  of  water,  37-43;  total 
hardness,  37-38;  temporary  and 
permanent,  38;  magnesiiyia  hard- 
ness, 42 

Harmful  colouring  agents  in  food, 
382-383 

Harmless   colouring   agents   in   food, 

383-385 
Heated  milk,  247-248 
Hehner  and  Richmond's  formula  for 

fat  in  milk,  238 
Hehner's  test  for  formalin,  375 
Hempel's  gas  burette,  175,  177 


Hesse's  apparatus  for  i.oll(;(  ting  sus- 
])ended  matter  of  air,  211;  lor  ( ol- 
iecting  ground  air,  219 

Honey,  342 

Horseflesh,  312-314 

Houzeau's  test  for  ozone,  208 

Human  milk,  227 

Hydatids,  300 

Hydrochloric  acid  in  air,  204 

Ice,  138-139 

Ice-creams,  bacteriological  examina- 
tion of,  311 
Ignition  of  solid  residue,  2,  61 
Ilosvay's  test  for  nitrites,  95 
Improvers  added  to  flour,  275 
Indicators,  33,  137 
Infants'  food,  357 
Infusorians  in  water,  6G,  71 
Ironin.water,  45,  47-4S,  51,  52-53 
Iso-nitril  test,  383 

Jams,  342 
Jean's  test,  260 

Kjeldahl's  process,  145-147,  165,  273- 

274 
Knopp's    sieves,     160;     soil-washing 
.    cylinder,  161 
Koumiss,  248 
Koppeschaar's  process,  400-401 

Lancet  methods:  testing  gas-fires, 
197-198;  tannin  in  tea,  356;  tar- 
acids,  401-402 

Lard,  265 

Lead  in  water,  44-45,  47-48,  50-51, 
52;  in  food,  362;  in  wall-papers, 
396 

Let! mann-Beam  process  (modified) , 
237-238 

Legler's  method  of  estimating  formic 
aldehyde,  377 

Lemon-juice,  335 

Lentil-flour,  284 

Leptomitus  lacteus  in  water,  57,  69 

Leptothvix  in  water,  69 

Leucocytes    in   milk,    231,    240-241, 

249 
Lie-tea,  354 
Lime-juice,  335 

Ling  and  Rendle's  indicator,  341 
Lithia  water,  139 
Living  animal  matter  in  water,   71- 

74 
Living    vegetable    matter   in    water, 

69-70 
Logwood,  3 S3 
Lolium  temulentum,  277 
Long  pepper,  338 


4i6 


LABORATORY   WORK 


Lunge  and  Zeckendorf 's  process  for 

COo  in  air,  1S6-187 
Lunge-Trillich  nicthotl  of  estimating  j 

free  COo  in  water,  101-102  ' 

Magnesium,    hardness    due    to,    42;: 
salts  in  water,  55-56 

Maize,  284,  2S9,  291 

Manganese  in  water,  50,  ^2 

Manures,  166 

Margarine,  254-2O0 

Marsh  air,  210;  gas,  195-196 

Marsh's  test  for  arsenic,  389-392 

Measly  beef,  299;  pork,  298 

Meat,  examination  of,  293-317; 
characters  of  good  and  bad,  293- 
297;  parasites  in,  297-304;  fish, 
295.  307,  310;  horseflesh,  312-314; 
sausages,  pork  pies,  etc.,  314-315; 
eggs,  315;  meat  preparations,  315- 

,   317 

Meat  essences,  316-317 

Meat  extracts,  315-316 

Meat-poisoning,  305-311 

Metals,  poisonous,  in  water,  44-53 

Metric  system  of  weights  and  meas- 
ures, 16-17 

Mildew,  2S0 

Milk,  225-252;  composition  of,  225- 
228;  of  diseased  cows,  228;  analy- 
sis, 229-241 ;  adulteration,  242-244 

Milk  preparations,  245-248;  milk 
standards,  24S-250;  bacteriological 
note,  250-252 

Mineral  waters,  139-140 

Mines,  air  of,  217-218 

Miniature  gallon,  23-24 

Mucor  mucedo,  70,  264,  270,  394 

INIustard,  336 

Mystin,  244,  376 

Naphthylamine  test  for  nitrites,  95 

Nesslerization,  81 

Nessler's  reagent,  77-78 

Nitrates  in  water,  92-100 

Nitrifying  organisms,  92;  in  soil,  159 

Nitrites  in  water,  92-98 

Nitrogen,  oxidized  in  water,  92-100; 

compounds  of,  in  air,  204-205,  222; 

in  food,  276 
Normal  solutions,  136-137 

Oatmeal,  284,  289-291 
Oidium  abortifaciens,  267-269 
Oidiiim  atirantiacum,  279,  280 
Oleo-margarine,  254-260 
Onchocerca  Gibsoni  in  flesh,  298 
Opinion  on  a  water  analysis,  1 13-129 
Organic  carbon  and  nitrogen,  90-91 
Orgcmic  matter,  destruction  of,  387 


Organic  matter  in  water,   75-76;  in 

air,  192-194 
Organisms  in  water,  68-74 
Oxidizable  organic  matter  in  water, 

80-90;  in  air,  194 
Oxidized  nitrogen  in  water,  92-100; 

in  sea-water,  132-135 
Oxygen,  absorbed  by  organic  matter 

in  water,   86-90;  in  air,   174-178; 

dissohcd  in  water,  104-109 
Oxyuris  vermiciilaris,  72,  74 
Oysters,  310-311 
Ozone,  206-209 
Ozonometry,  209 

Paraffin  in  lard,  265 

Parasites,  human,  in  water,  72-74; 
of  cheese,  264-265;  of  corn,  266- 
270;  of  meat,  297-304 

Pea-meal,  284,  288 

Peat  in  water,  26,  30,  118 

Peaty  acids  in  water,  30,  40;  in  soil, 
165 

Peaty  soil,  163,  172 

Penicillium  glancum,  70,  270,  280; 
P.  brevicauie,  394 

Pepper,  336-338 

Pepper  brand,  269 

Perchloride  of  mercury  as  disinfect- 
ant, 405 

Permanganate,  estimation  of  strength 
of,  405 

Peroxide  of  hydrogen  in  air,  209;  as 
an  antiseptic,  244,  381 

Pettenkofer's  estimation  of  COo  in 
air,  180-186 

Phenols  in  carbolic  powders,  402-403 

Phenol-sulphonic  acid  test  for  nitrates 
in  water,  99-100 

Phosphates  in  water,  58-59;  in  sea- 
water,  133,  135;  in  soil,  164 

Phosphuretted  hydrogen  in  air,  204- 
205 

Plastering  of  wines,  326-327 

Poisonous  fungi,  312 

Poisonous  metals  in  water,  44-53 

Poivrette,337-338 

Polariscope,  12-15 

Polenske's  process,  259-260 

Polishings  of  rice,  291-292 

Pork,  measly,  298 

Potass  water,  139 

Potato -flour,  285,  288;  poisoning, 
308 

Pouchet's  aeroscope,  211 

Prepared  cocoa,  348 

Preservatives  used  in  food,  364-382 

Preserved  provisions,  358-365 

Proof-spirit,  319 

l^rotozoa  in  water,  71 


INDEX 


417 


Provisions,    tinned    and    preserved, 

358-365 
Psorospermia,  302-303 
Ptomaines  in  food,  305-307 
Puccinia  graminis,  270 
Putrefaction  in  llesh,  295-296 

Rag-flock,  examination  of,  396-397 

Rainey's  capsules,  302-303 

Rain-water,  31,  117 

Ray-fungus,  303-304 

Reaction  of  water,  29-30;  of  air,  173; 

of  milk,  230 
Reductase  test  in  milk,  249-250 
Reichert's  process  for  butter  analysis, 

256-259 
Reinsch's  test  for  arsenic,  388-389 
Residue,  solid,  of  water,  60-63 
Revis's  test  for  benzoic  acid  in  milk, 

379 
Rice,  285,  288 
Richmond    and    Hehner's    formulse 

(milk),  234,  238 
Rideal- Walker  test,  407-411 
River-mud,  122,  155,  166 
River-water,  119 
Rose's  test  for  fusel-oil,  324-325 
Round-worm,  the,  72-74 
Royal     Commission     on     Arsenical 

Poisoning,  388 
Rum,  319,  325 
Rust  in  wheat,  270 
Rye-meal,  285,  288,  290 

Saccharine,  380 

Sago,  284,  289 

Salicylic  acid,  327,  366,  368,  378-379 

Sausages,  314-315 

Scheme  for  quick  analysis  of  water, 
140-141;  for  detecting  large  quan- 
tities of  gases  in  air,  221-223 

Schmidt's  process  for  fat  in  milk, 
234-236 

Schulze's  method  of  soil  analysis,  163 

Sea-water,  36,  130-135 

Sediments  in  water,  30,  64-74;  ^^ 
milk,  231-232 

Seltzer-water,  139 

Seminormal  solutions,  136 

Separated  milk,  245 

Sesame  oil,  261-262 

Sewage  effluents,  143-154;  standards 
of  purity  of,  147-150 

Sewage  fungus.     See  Beggiatoa  alba 

Sewage-polluted  mud,  155 

Sewer-air,  216-217 

Shell-fish,  307,  310 

Silica  in  water,  56 

Skimmed  milk,  245 

Smut  in  wheat,  269 


Soda-water,  139 

Soil,  157-172;  chemical  examination 
and  analysis  of,  157-168;  classifica- 
tion of  soils,  159-163;  bacterio- 
logical examination  ol,  168-171 

Solid  residue,  collection  and  weigh- 
ing, 5-6;  of  water,  60-63 

Soot  in  air,  214 

Sour  milk,  238-240 

Soxhlet's  fat  -  extraction  apparatus, 
9-10 

Specific  gravity  test,  6-9;  of  butter- 
fat,  6-8,  256 

Spectroscope,  11- 12 

Sphcsroiilus  natans  in  water,  57,  69 

Spices,  336-338 

Spirits,  319-325 

Sporendonema  casei,  264 

Standard  flour,  271 

Starch,  characters  of  granules,  285- 
289;  in  infants'  foods,  357;  in 
cream,  244 

Starch  test  (nitrites),  95 

Stas'  method  for  alkaloids,  310 

Streptococci  in  water,  126-128;  in 
soil,  168-171;  in  air,  220;  in  milk, 
241 

Strongylus  filaria,  297;  5.  paradoxi- 
cus,  297;  5.  micrurus,  297;  S. 
rufescens,  297 

Sugar,  338-342;  amount  of  sugar 
present  in  any  substance,  340-341 

Sugar-mite,  339 

Sulphates  in  water,  57-58 

Sulphuretted  hydrogen  in  water,  28, 
29,  85, 103,  139 ;  in  air,  203-204,  222 

Sulphuric  acid  in  air,  202-203 

Sulphurous  acid  in  air,  202-203,  222; 
as  an  antiseptic  in  food,  330,  368, 
380-381 ;  as  a  disinfectant,  405 

Surface  waters,  iio-iii 

Suspended  matter  in  water,  64-74; 
in  sewage  effluents,  145,  149;  in 
air,  210-215 

Synthetic  milk,  248 

Tabellaria  in  water,  27,  28,  70 

Table  jellies,  317 

TcBfiia  echinococcus,  72,  74,  300;  T. 
solium,  298-299;  T.  niediocanellata, 
299;  T.  nana,  300;  T.  cucumerina, 
300;  T.  cosniiriis,  297;  T.  marginata, 
297 

Tannin  in  wine,  327;  in  tea,  356-357 

Tapioca,  284,  289 

Tar-oils  in  crude  carbolic  acid,  402 

Tar    preparations,    as    disinfectants, 

399 
Tea,  350-357;  characters  of  the  leaf, 
352;  adulteration,  351-357 


4if 


LABORATORY    WORK 


Temporary  ami  permanent  hardness, 

37-43 
Textile  fibres,  6S-69 
Thein,  350,  355-35<> 
Theobromine,  348-349 
Thorpe's  method  of  estimating  COo 

in  water,  102-103 
Thread-worm,  the,  72,  74 
Thresh's  test  for  dissolved  oxj'gen  in 

water,  104-108 
Tidy's  process  in  water  analysis,  86- 

90 
Tilletia  caries,  269;  T.  IcBvis,  269 
Tin  in  water,  46,  49;    in  food,  361- 

362 
Tinned  provisions,  358-365 
Total  solids  in  water,  60-03;  volatile 

and  non-volatile,  61-62 
Trichina  spiralis,  301-302 
Trichocephalus  dispar,  72-74 
Turmeric,  244 
Tyrotoxicon,  308-309 

Ulva  latissima,  131,  154-155 
Upland  surface  water,  iio-iii 
Uredofcelida,  269;  U.  segetum,  269 
Uroglena  in  water,  29 

Valenta  test  for  butter,  260 

Vanillin,  308 

Vibriones  in  wheat,  266-267 

Vieth's  ratio,  226 

Vinegar,  332-334 

Vogel's  test  for  CO  in  air,  198-199 

Volatile  disinfectants,  test  of,  411 

Wanklyn,  Chapman,  and  Hall  pro- 
cess, 76-85 

Water,  collection  of  samples  of,  19- 
21 ;  information  required  as  to 
samples,  21-22;  report  on,  22-23; 
opinion  on,  11 3-1 29;  physical  char- 
acters, 25-30;  clearness,  25;  colour. 


25-27;  taste,  27;  odour,  27-29; 
aeration,  29;  reaction,  29-30;  tem- 
perature, 30;  chlorine,  31-36;  hard- 
ness, 37-43;  poisonous  metals,  44- 
53;  non-poisonous  metals,  54-56; 
sulphates,  57-58;  phosphates,  58- 
59;  solid  residue,  60-63;  suspended 
and  deposited  matter,  30,  64-74; 
orgixnic  matter,  75-76;  Wanklyn's 
process,  76-S5;  oxidizable  organic 
matter,  86-90;  Frankland's  pro- 
cess, 90-91 ;  oxidized  nitrogen,  92- 
100;  gases  in,  101-109;  water  from 
various  sources,  110-113;  opinion 
on  water  samples,  11 3- 129;  water 
standards,  114-116,  123-129;  "bac- 
teriological evidence,  123-129; 
scheme  for  water  analysis,  140-141 

Water-bath,  5-6 

Weevil,  266 

Weighing,  operation  of,  3-5 

Weights  and  measures,  16-17 

Well-water,  deep,  111-113,  liS,  120 

Werncr-Schmidt  process,  234-236 

Westphal  balance,  8-9 

Wheat-flour,  composition  of,  270-271 ; 
analysis,  271-275;  adulteration, 
275-277;  microscopical  characters, 
287,  290 

Whip-worm,  the,  72,  74 

Whisky,  319.  322 

Wiley's  experiments  on  chemical 
antiseptics,  368-369 

Wills'  combined  water-bath  and 
drying -oven,  2 

Wine,  325-329 

Winkler's  process  for  dissolved  oxy- 
gen in  water,  108-109 

Wood  acid,  332 

Wynter  Blyth's  tube  for  sediments, 
64-65 

Zinc  in  water,  45-46,  49,  51-52 


H.     K.    LEWIS,    136,    GOWF.R    STREET,    1.0NU0N 


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